Maine Lakes Report 2012 - Lake Stewards of Maine
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Maine Lakes Report
2012
Dear Friends of Maine Lakes,
This report on the health of Maine lakes reflects the effort of more than 1,000 volunteer citizen scientists
who monitored several hundred lake basins throughout the State in 2012. Many of them have been
doing so continuously for decades, and a few have been involved for most of the 42 years since the Maine
Legislature officially authorized volunteer lake monitoring. Their work is a strong testimony to the level of
public commitment in Maine to our clear, clean lakes, and it is probably not coincidental that our lakes
have remained as healthy as they have under the watch of these individuals.
The Maine Volunteer Lake Monitoring Program (VLMP) is believed to be the longest-standing statewide
citizen lake monitoring program in America, having been formed at about the time of the passage of the
historic Federal Clean Water Act.
The Mission of the Maine Volunteer Lake Monitoring Program is to help protect Maine lakes through
widespread citizen participation in the gathering and dissemination of credible scientific information
pertaining to lake health. The VLMP trains, certifies and provides technical support to hundreds of
volunteers who monitor a wide range of indicators of water quality, assess watershed health and function,
and screen lakes for invasive aquatic plants and animals. In addition to being the primary source of lake
data in the State of Maine, VLMP volunteers benefit their local lakes by playing key stewardship and
leadership roles in their communities.
Our primary partners are the Maine Department of Environmental Protection (DEP) and the US
Environmental Protection Agency, which provide a wide range of financial, technical and management
support to the program. In turn, the VLMP provides these agencies with essential information that they
use to manage and protect Maine’s lakes.
The relatively small investment of public funding that supports the work of the VLMP is multiplied
in value several times through the invaluable, high quality work of VLMP volunteers, and from
increasing private support from individuals, organizations and businesses who recognize the
tremendous benefits to Maine lakes. Studies conducted throughout the country have consistently
shown that lake data gathered by properly trained volunteers are equivalent to, and indistinguishable
from that of professional lake scientists, at a fraction of the cost! The additional invaluable benefit of
public education and stewardship that VLMP volunteers provide to communities throughout the state is
one of Maine’s best examples of grassroots natural resource protection.
The effectiveness and strength of the VLMP is in part due to collaborative partnerships with other entities,
including agencies and organizations throughout Maine and the U.S. This collaboration has formed a
powerful resource for technical expertise, outreach, and access to a great deal of information concerning
Maine lakes and their watersheds.
Since the earliest days of the program, the VLMP has been at the forefront of gathering lake data in Maine
and the U.S. For more than four decades, the total number of active individuals involved in monitoring
water quality, and in screening public waters for invasive aquatic species has increased steadily. This
document is a testament to their remarkable commitment!
Volunt
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Scott Williams
Lake
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VLMP Executive Director
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Maine Lakes Report
2012
Acknowledgements
Written by: Layout: Contributors & Reviewers:
Scott Williams Jonnie Maloney Linda Bacon
Roberta Hill Roberta Hill
Database/Computer Technical Scott Williams
GIS/Mapping: Assistance: Jonnie Maloney
Linda Bacon Linda Bacon Christine Guerette
John McPhedran Christine Guerette
Doug Suitor Jonnie Maloney
VLMP Staff VLMP Advisory Board
Scott Williams, Executive Director Holly Ewing
Roberta Hill, Invasive Species Program Director C. Barre Hellquist
Jonnie Maloney, Program Coordinator Martha Kirkpatrick
Christine Guerette, Program Assistant David Littell
Cat Dioli, 2012 Spring Intern Peter Vaux, Chair
Deanna Lorenzo, 2012 Spring Intern Ken Wagner
Garrison Beck, 2012 Summer Intern Pixie Williams
Jamey Epstein, 2012 Summer Intern
Maine DEP Technical Advisors
Linda Bacon
VLMP Board of Directors
Paul Gregory
Mary Jane Dillingham, President Karen Hahnel
Bill Monagle, Vice President John McPhedran
Lew Wetzel, Treasurer Judy Potvin
Phoebe Hardesty, Secretary
Malcolm Burson Cover: Mud Pond, Oxford
George Cross
Sibyl French
Norton Lamb
Bill Monagle
Gerry Nelson
Matt Scott
Clyde Walton
Linda Bacon, DEP Liaison
Photo by Terri Coolidge Marin
Maine VLMP 207-783-7733
24 Maple Hill Rd vlmp@mainevlmp.org
Auburn, ME 04210 www.MaineVLMP.org
Copyright © 2013 Maine Volunteer Lake Monitoring Program
This report is printed on recycled paper.
Table of Contents
Overview 2013 VLMP Program Updates . . . . . . . . . . . . . . . . . . . 26
Volunteer Coordinators . . . . . . . . . . . . . . . . . . . . . . i Appendix
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 A Distribution of Water Quality Data
Program Purpose & Goals . . . . . . . . . . . . . . . . . . . . 2 for Maine Lakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Program Structure & Administration . . . . . . . . . . . 2 B Water Quality Data for VLMP Lakes . . . . . . . . . . . 33
Water Quality C Range of Average Secchi Disk
Transparency for VLMP Lakes . . . . . . . . . . . . . . . . 45
How are the Water Quality Data Used? . . . . . . . . 4
Volunteer Training, Quality Assurance & D Explanation of Individual Lake Report
Quality Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 and Sample Lake Report���������������������������������������
. . . . . . . . . . .������������������
. . . . . . . . . 53
How do Volunteers E Invasive Aquatic Plant
Monitor Water Quality? . . . . . . . . . . . . . . . . . . . . . . 6 Screening Survey Activity . . . . . . . . . . . . . . . . . . . . 58
Measuring Lake Water Quality F Certified Volunteer Monitors . . . . . . . . . . . . . . . . . 67
With a Secchi Disk . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
G Lifelong Volunteers . . . . . . . . . . . . . . . . . . . . . . . . . 85
Monitoring Dissolved Oxygen &
Lake Water Temperature . . . . . . . . . . . . . . . . . . . . . 9 Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Monitoring Total Phosphorus 2012 VLMP Supporters . . . . . . . . . . . . . . . . . . . . . . . . . 92
Concentrations in Lakes . . . . . . . . . . . . . . . . . . . . . 10
Advanced Lake Monitoring . . . . . . . . . . . . . . . . . . 11
2012 Season in Review . . . . . . . . . . . . . . . . . . . . . . 12
Invasive Aquatic Species
Purpose & Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Invasive Plant Patrol Training,
Quality Assurance & Quality Control . . . . . . . . . . 17
Invasive Aquatic Plant Screening Surveys . . . . . . . 18
How are Plant Survey Data Used? . . . . . . . . . . . . . 20
2012 Season in Review . . . . . . . . . . . . . . . . . . . . . . 20
Invasive Aquatic Plant Survey Summary . . . . . . . 22
Known Infestations . . . . . . . . . . . . . . . . . . . . . . . . . 22
Invasive Plant Patrol Leadership . . . . . . . . . . . . . . 24
Support for this report has been provided by:
US Environmental Protection Agency Maine Department of
through Section 319 of the Environmental Protection
Federal Clean Water Act
Boater Participation in the Maine Lake & River Protection Sticker Program
Ram Island Conservation Fund of the Maine Community Foundation
Roy A. Hunt Foundation
More than 1,000 volunteer lake monitors throughout Maine who have provided their time, expertise, and financial support.
2012 Volunteer Coordinators
Regional Water Quality Regional Invasive Plant
Volunteer Coordinators Patrol Coordinators
Regional Coordinators (RC) Invasive Plant Patrol Coordinators help organize volunteers and training
RC’s organize re-certification workshops, respond to workshops in their region. Additional duties may include providing regional
requests from volunteers and assist in the collection technical support, coordinating Invasive Aquatic Plant screening survey
of data. activity, and managing data collection.
Data Coordinators (DC) Region Coordinator(s)
DC’s enter water quality data collected on volunteer data
Aroostook County
forms into the VLMP’s LakeData database program. Island Falls Lake Association Norm Harte
Regional and Data Coordinators commit 25 hours on average Hancock County Region
per year to the program. If you are interested in volunteering Hancock SWCD and
Hancock County Lakes Alliance Megan Facciolo
for a Coordinator position, please contact the VLMP office.
Kennebec County
30 Mile River Watershed Association Lidie Whittier Robbins
Belgrade Regional Conservation Alliance Toni Pied
Region Coordinator Friends of the Cobbossee Watershed Ken Smith
Androscoggin Dan Guerette, RC Midcoast Region
Alan Anderson, DC Acadia National Park Bill Gawley
Aroostook VLMP Staff, RC & DC Citizens’ Association of Liberty Lakes Kerry Black, Linda Breslin
Cumberland Charles Turner, RC Damariscotta Lake Watershed Association Julia McLeod
VLMP Staff, DC Lincolnville Lakes and Ponds Committee Ken Bailey / Paul Leeper
Pemaquid Watershed Association Donna Minnis
Franklin VLMP Staff, RC
Lew Wetzel, DC Penobscot County Region
Baxter State Park Jean Hoekwater
Hancock VLMP Staff, RC & DC University of Maine Cooperative Extension Laura Wilson
Kennebec Sue & Bruce Fenn, RC & DC
Knox Dave Preston, RC Rangeley Lakes Region
VLMP Staff, DC Rangeley Lakes Heritage Trust Rebecca Kurtz, Ellie White
Lincoln Ed Knapp, RC Southwestern Maine Region
Steve O’Bryan, DC Lakes Environmental Association Colin Holme
Lakes Coalition Cheryl Welch
Oxford Art Bubar, RC
Lovell Invasive Plant Prevention Committee Lucy LaCasse
Joe Potts, DC Pleasant Lake and Parker Pond Assoc. Pixie Williams
Penobscot VLMP Staff, RC Portland Water District Nate Whalen
David Hodsdon, DC Raymond Waterways Protective Association Steve McCormack / Betty
Piscataquis VLMP Staff, RC Williams, Sibyl French
Richard Offinger, DC Saco River Recreation Council Michelle Broyer
Sagadahoc Ed Knapp, RC York County
Steve O’Bryan, DC Acton Wakefield Watershed Alliance Linda Shier
York County SWCD Melissa Brandt, Laurie Callahan
Somerset VLMP Staff, RC
Lew Wetzel, DC
Waldo VLMP Staff, RC & DC
Washington VLMP Staff, RC
Richard Offinger, DC
York George Bouchard, RC
VLMP Staff, DC
Acadia National Park Bill Gawley, RC
Allagash Wilderness Kevin Brown, RC
Waterways VLMP Staff, DC
Cobbossee Watershed Wendy Dennis, RC & DC
District
Lakes Environmental Assoc. Colin Holme, RC & DC
Passamaquoddy Nation Joe Musante, RC & DC Volunteers play key leadership roles in the VLMP. Here, Invasive Plant Patrol
Rangeley Lakes Rebecca Kurtz, RC Lake Team and Regional Leaders convene for the spring IPP Roundtable.
Heritage Trust VLMP Staff, DC
i
VLMP Program Overview
Mission:
The Mission of the Maine Volunteer Lake Monitoring Program is to help protect Maine lakes through widespread citizen
participation in the gathering and dissemination of credible scientific information pertaining to lake health. The VLMP trains,
certifies and provides technical support to hundreds of volunteers who monitor a wide range of indicators of water quality,
assess watershed health and function, and screen lakes for invasive aquatic plants and animals. In addition to being the
primary source of lake data in the State of Maine, VLMP volunteers benefit their local lakes by playing key stewardship and
leadership roles in their communities.
Introduction
Maine’s 5,785 lakes and ponds, about half of which are
in the public domain, are among the most pristine in the
nation. Lake scientists have long recognized that protect-
ing and keeping lake ecosystems healthy requires knowl-
edge of a large and broad cross-section of waterbodies. For
42 years, Maine’s Volunteer Lake Monitoring Program has
risen to the challenge by collecting a substantial percentage
of the annual water quality data for Maine lakes. As new
threats have presented themselves, such
�������������������������
as invasive aquatic
species, VLMP
���������������������������������������������
volunteers have expanded their level of
commitment and stewardship.
Recognition of the relationship between healthy lakes
and Maine’s economy is well established. Information
collected by VLMP volunteers has greatly contributed to
this understanding. In 2012, volunteers collected water
quality data from 415 Maine lakes across the state. As of
Volunteers receive training and are certified through the
2012, 449 waterbodies across the State of Maine have also
VLMP. Depending on personal interests and program
been screened, at some level, for the presence of aquatic
needs, a number of training and monitoring options are
invaders. A high percentage of the screening surveys were
available. Hundreds of volunteers are trained to monitor
conducted by volunteers trained by the VLMP.
lake transparency (water clarity) using a simple Secchi
Established in 1971, the VLMP, first administered by disk. Some monitor more advanced water quality indica-
the Maine Department of Environmental Protection tors, including total phosphorus, dissolved oxygen, chlo-
(DEP), became an independent non-profit organization rophyll-a and more. And others are trained to conduct
in 1992. A strong cooperative and mutually beneficial screening surveys for aquatic invaders. Many volunteers
relationship has been maintained between the VLMP provide data concerning additional characteristics of their
and the DEP ever since. We are a valuable resource to lakes, including “ice-out” dates, the presence of certain
the state, while the DEP continues to provide quality forms of troublesome algae, and more.
assurance and quality control oversight, assists us with
Training, basic equipment and technical support are
data management, and provides technical expertise to
provided by the VLMP at no charge, in return for a
VLMP staff and volunteers.
commitment from volunteers to monitor their lakes. All
Funding for the VLMP is provided through contributions volunteers receive ongoing technical support for as long
from individuals, businesses, and grassroots watershed as they are active in the program. Questions concerning
groups, as well as grants from the EPA, Maine DEP, and procedures, data collected, the interpretation of results,
private charitable foundations. But the greatest value of the algae and invasive plant identification, presenting lake
VLMP comes from the efforts of hundreds of volunteers data to watershed communities, and more, are frequently
who contribute thousands of hours of their time annually, addressed by VLMP technical staff. Individual contact and
and who are the backbone of the Program. support is an essential component of insuring the credibil-
ity of lake data collected by volunteers.
Overview 
Map by: Linda Bacon & port the work of those other efforts at the state, regional and
Doug Suitor; Maine DEP local levels. Reliable information about Maine lakes, both
individually and collectively, is the foundation of all efforts
to protect, manage and restore these resources.
Program Structure and
Administration
The VLMP is structured to optimize volunteer participation
in both data acquisition and program administration.
This reduces the cost of operations, increases feedback to
program administrators from volunteers, and strengthens
local stewardship.
The VLMP is governed by a volunteer Board of Directors.
The Board has approved by-laws and a regularly updated
Strategic Plan. Board meetings are held several times
throughout the year and are open to the public.
The VLMP also has volunteer Regional and Data
Coordinators that assist with program management at
various levels by organizing re-certification workshops,
collecting data forms, entering data into the data-
Maine Lakes with base, maintaining contact info for the volunteers, and
VLMP Volunteer Monitors in 2012 responding to volunteer requests for equipment and
monitoring forms. Each of the 16 counties in Maine has
its own Regional Coordinator, and there are several local
The VLMP is Maine’s leader in providing training and cer- organizations such as Cobbossee Watershed District,
tification in the collection of lake data by volunteers, state Lakes Environmental Association, and Rangeley Lakes
agency personnel, educators, consultants and others. Heritage Trust that function as Regional Coordinator for
volunteers in their service area.
Program Purpose and Goals Volunteer training and re-certification workshops are
The VLMP fosters stewardship of Maine lakes and their offered during the spring and summer monitoring period.
watersheds in order to ensure high water quality and VLMP and Maine DEP staff travel throughout Maine
ecological integrity. This is accomplished by the collection to meet with volunteers, provide them with training,
of credible lake data by trained citizen volunteers, and by equipment and technical support.
providing educational information concerning lakes to the The VLMP is funded by diverse sources, including indi-
citizens of Maine. viduals, grassroots lake and watershed groups, state and
The VLMP develops and disseminates educational mate- federal agencies, charitable foundations and businesses.
rials concerning various aspects of lakes and their water-
Maine Volunteer Lake Monitoring Program
sheds, including water quality, ecology, management,
protection and stewardship. The VLMP acts as a liaison,
when possible, to bring together groups and organiza- Regional & Data DEP Technical
Coordinators Advisors
tions with missions similar to ours to maximize the ben-
efits of collaborative synergy.
Volunteer
A number of organizations work on behalf of Maine’s Monitors
lakes and ponds. Some focus specifically on advocacy;
others primarily on public education. To some extent,
the VLMP mission overlaps with those of other entities. VLMP Staff &
All are working in various ways to protect lakes. What sets Board of Directors
the VLMP apart is the particular role the organization plays
within this larger statewide effort, a role that helps to sup-
Overview
The annual Maine Lakes Report is made available to summer. The event also features presentations on a wide
our volunteers and is also on our website. Annual water range of technical issues pertaining to lake monitoring,
quality reports for individual lakes are also available to assessment and protection.
volunteers and the public.
The Water Column, VLMP’s
newsletter, is distributed twice
annually to program volunteers
and collaborating organizations,
and is available online.
The VLMP's Annual Lake
Monitoring Conference, at
which individuals are recognized
for their contributions to Maine
lakes, is held annually during the
Agencies and Organizations Working in Collaboration with the VLMP
Acadia National Park Maine Department of Conservation Natural Areas Program
Allagash Wilderness Waterways Maine Department of Environmental Protection
Auburn Land Lab Maine Department of Inland Fisheries and Wildlife
Auburn Water District Maine Milfoil Initiative
Belgrade Regional Conservation Alliance Maine Stream Team
Casco Bay Estuary Partnership Maine Water Utilities Association
Cobbossee Watershed District Passamaquoddy Tribe of Maine
County Soil and Water Conservation Districts Penobscot Nation
Friends of the Cobbossee Watershed Portland Water District
George J. Mitchell Center - University of Maine Rangeley Lakes Heritage Trust
Gulf of Maine Research Institute Raymond Waterways Protective Association
Hancock County Lakes Alliance Saco River Corridor Commission
Lake & Watershed Associations throughout Maine Saco River Recreation Council
Lake Auburn Watershed Protection Commission Sebago Lake State Park
Lakes Environmental Association The Nature Conservancy
Maine Audubon Society Trout Unlimited
Maine BASS Federation University of Maine
Maine Congress of Lake Associations University of Maine - Cooperative Extension
Maine Department of Conservation US Environmental Protection Agency
Volunteer trainings are held annually throughout Maine, as well as at
VLMP's Brackett Environmental Center on the shore of Lake Auburn.
Overview 
Monitoring Lake Water Quality
How are the Water Quality Data Used?
Lake Diagnostic Studies
Data collected by volunteer water quality monitors provide
valuable information to lake scientists at the Maine DEP, Each lake has a unique history and "personality." Data
the EPA, the University of Maine, public water utilities collected by VLMP allows the Maine DEP and others to
and other agencies and institutions throughout Maine in determine the nature and sources of water quality prob-
order to help characterize and protect Maine lakes. State lems for individual lakes, and the most effective means for
and town planners, conservation groups, economists, lake restoring and protecting them from further decline.
associations, businesses, and individuals also use the data.
Lake Restoration Projects
Data Users Efforts to restore a lake that has declined requires extensive
Maine Department of Environmental Protection (DEP) water quality data. Long-term restoration also involves
and other state agencies addressing land use problems in the watershed. The
US Environmental Protection Agency (EPA) VLMP and DEP work with volunteer monitors, local lake
University of Maine and other educational institutions
associations, and watershed communities to identify means
County Soil & Water Conservation Districts
by which sources of
Water Utilities
pollution to lakes
Towns, Local Planners and Businesses
Lake and Watershed Associations
can be identified
and eliminated. This
VLMP lake data, and data obtained through a collabora- is accomplished
tive effort with the Maine DEP and other agencies and through lake and
organizations, are the primary sources of water quality watershed education
information for Maine lakes. The following are just a few and outreach
of the ways in which the data are used: services, and by
working with groups Lakes that have become choked with excess algae
Research to implement lake growth may require restoration measures that
range from the application of simple watershed
Scientists and researchers use VLMP data to characterize and watershed conservation practices to prohibitively costly,
the quality of individual lakes, and to identify water protection projects. and risky, in-lake treatment measures.
quality trends. A number of agencies and institutions
in Maine use this information to help determine the Lake Protection
economic benefits provided by lakes, and the potential Town planning boards, lake associations, conservation
loss of these benefits when water quality declines. Recent commissions and others use water quality data to develop
economic studies using VLMP data have linked lake local standards for lake protection. The Maine DEP uses the
water clarity to shoreline property values. information to establish phosphorus control standards for
individual lakes. VLMP data have been used to determine
State agencies use VLMP data to assess fishery habitat. the "Lakes Most at Risk" for the Maine Stormwater
For example, dissolved oxygen data are used to determine Management Law, and for establishing "Priority Lake
the extent to which individual lakes are able to support Watersheds" for Maine's Nonpoint Source Program. The
coldwater species, and whether or not fishery habitat is Federal Clean Water Act requires states to evaluate the
changing with time. status of their lakes and report the results to the EPA, and
Understanding the relationship between watershed land Maine's Water Classification Program requires a similar
use and lake water quality is key to protecting lakes. assessment. VLMP data are used extensively for this
VLMP data are used to further our understanding purpose. (See Appendix B for details.)
of this relationship, and help determine appropriate
Outreach and Technical Assistance
standards for lake protection by federal, state and local
planners. The information is also used to develop public The VLMP provides data, analysis, and training to those
educational materials. across Maine interested in understanding and protecting
lake water quality, and preventing the introduction of
Water Qualityinvasive aquatic plants. Many schools throughout Maine Individuals who collect and submit Maine lake data to the
use VLMP lake data. The VLMP is a resource to educational VLMP and DEP, regardless of whether they are volunteers
institutions with lake studies programs, from elementary or professionals, must be certified. Becoming certified to
grades through graduate studies. The VLMP staff works collect water quality data entails a comprehensive train-
with lake associations and organizations like the Maine ing process. Volunteers are required to attend an initial
Congress of Lake Associations to help those who have an workshop at which they are provided with information
interest in understanding and protecting lakes to achieve concerning lake function and ecology, lake and watershed
their goals. The real estate industry and tourism-based relationships, perspective on various threats to lakes, moni-
businesses have a vested interest in the quality of Maine toring protocol and procedures, and direct field experience
lakes. The VLMP works with numerous local and state in the gathering of data. Individuals and the equipment
business groups to provide water quality and economic that they use are evaluated, and their data are recorded
analysis information to the business community. Fishing for future reference. Each individual is assigned a unique
organizations such as Maine BASS Federation also partner certification number to link them to any and all data that
with the VLMP to protect Maine's fishing heritage from they submit to the VLMP or Maine DEP.
the threat of invasive aquatic plants.
Volunteers are required to periodically attend re-certification
Legislative Initiatives workshops that are held throughout Maine annually. Re-
As an important source of quality data and objective certification requirements vary, depending on the type of
information, the VLMP provides the Maine Legislature data being collected. Workshops provide volunteers and
with objective testimony concerning critical issues relating staff with opportunities to discuss technical issues and
to Maine lakes. However, in order to protect the integrity questions, changes in protocol, the analysis of data, and
of the data, the VLMP does not advocate for or against to inspect monitoring equipment. Volunteers and staff
(lobby) specific political initiatives. The VLMP is an also review data gathering procedures, take readings and
apolitical organization. compare results. The workshops also provide volunteers
with an opportunity to provide feedback to staff on various
Volunteer Training, and Quality aspects of the program.
Assurance and Quality Control
All data, including volunteer-collected information, are
useful only when accurate, of acceptable quality, and
reliably collected. In order to ensure that the lake water
quality data collected by the VLMP are credible, all
Photo by Linda Bacon
contributors of this data must meet specific technical
standards. This system of quality assurance, and the
standards that must be followed by volunteers, staff and
others who participate in the gathering and processing
of data, is commonly known as "QA/QC" (quality Volunteer water quality monitors review Dissolved Oxygen monitoring
assurance/quality control). The VLMP standards of procedures with VLMP staff at a re-certification workshop on Long Lake.
quality assurance are defined in a plan that is approved
Quality �������������������������
Assurance/Quality Control
by the EPA (referred to as a Quality Assurance Project
The program accepts data only from monitors who are able to
Plan, or QAPP). Such a plan is required of all entities meet Quality Assurance/Quality Control standards. This strict
that receive funding from the EPA for data collection. rule affirms the credibility of the VLMP as an organization,
It assures that those who use the volunteer data may as well as the value and utility of the data. It allows the data
do so with confidence. The QAPP is available on our gathered by our volunteers to be used with confidence, and
assures volunteers that their monitoring efforts are well spent.
website at: www.MaineVolunteerLakeMonitors.org, on
the "Water Quality Monitor Forms and Procedures"
page. The primary role of the Maine DEP partnership
with the VLMP is to provide QA/QC guidelines and
standards for data collection and management. The
DEP staff serve as quality control agents, providing
technical support to VLMP staff, as required. The
VLMP and DEP staff work cooperatively to ensure that
available resources are used efficiently.
Water Quality How Do Volunteers Monitor Lake The enrichment of lakes with the nutrient phosphorus
and excess algae, resulting from watershed development, is
Water Quality? referred to as "cultural eutrophication" (CE). Stormwater
There are many imminent threats to Maine lakes. Near runoff from disturbed or developed areas of lake water-
the top of the list, and perhaps the most pervasive, is the sheds typically carry high concentrations of phosphorus,
potential for lakes to become nutrient enriched and more sediment particles, and other pollutants considerable
biologically productive as a result of development in lake distances, eventually flowing into a lake. Lake watershed
watersheds. This condition is characterized by declining boundaries may be situated close to the shoreline, or they
water clarity (transparency), resulting from an increase in may extend for miles away from the lake. In either case,
the growth of algae. Excess algae in lake water can cause stormwater runoff from developed areas of lake watersheds
is a potential threat to water quality, unless conservation
Watersheds & practices are in place to control stormwater runoff.
Water Quality For this reason, the primary focus of volunteer water
The Damariscotta Lake quality monitoring is the collection of information related
watershed encompasses
an area of more than
to changes in lake biological productivity over time.
50 square miles in five Water quality data gathered by volunteers can be used to
communities and extends determine whether individual lakes are becoming more
miles from the lake shore.
Storm water runoff from productive, less productive, or are stable. Many years of
developed areas within the data are generally required to make these determinations
watershed can carry soil
and other nonpoint source with confidence.
pollution into the lake.
Measuring Lake Water Clarity
(Transparency) With A Secchi Disk
One simple method of assessing the effect of cultural
eutrophication in lakes is to measure the concentration
of planktonic (suspended) algae in the water. Algae are
at the base of the lake ecosystem food web. Volunteer
water quality monitors begin monitoring their lake by
measuring Secchi disk transparency. The Secchi disk is a
simple device that is used to estimate algal concentrations,
a disturbance to the normal equilibrium of the aquatic based on water clarity. Volunteers in the VLMP are
ecosystem. As algae die and decompose, bacteria con- provided with a viewing scope and a Secchi disk that is
sume oxygen that is dissolved in the water. Increased algal attached to a calibrated line. They are instructed on the
growth can lead to a decline in oxygen levels, especially procedure for taking a Secchi disk reading by training
during the warm summer months. Oxygen loss can reduce staff. Ideally, readings should be taken a minimum of
critical habitat for coldwater fish (trout and salmon), and twice monthly from May through September or October.
it can accelerate the decline of water quality. This frequency is optimum for identifying water quality
Oligotrophic Mesotrophic Eutrophic
low productivity moderate productivity high productivity
Cultural Eutrophication
The enrichment of lakes with nutrients, sediment and algae from human activities, resulting in
increasing biological productivity and an acceleration of the natural aging process of the lake.
Images Courtesy of University of Wisconsin Extension
Water Qualitytrends over time. Readings are generally taken at the penetration into the water column is substantially attenu-
deepest point in a lake. ated. Shallow lakes may be subject to moderate concen-
trations of re-suspended bottom sediments in the water
The Secchi disk is generally a reliable device for quickly column, resulting from wind turbulence. Both color and
and inexpensively assessing lake water quality. The primary sediment can limit the utility of Secchi transparency data
uses of Secchi transparency data are: 1) to characterize or as an indicator of biological productivity. However, for
define the existing water quality of a lake, and 2) to iden- most Maine lakes, Secchi transparency is a reliable and
tify and track long-term water quality trends. relatively accurate method for assessing water quality.
How a Secchi Disk Measures Water Clarity Seasonal Changes in Secchi
(Transparency) Transparency
The Secchi disk is used globally to assess lake water
The tiny plants (algae or phytoplankton) and animals (zoo-
quality because it is a quick procedure that can be
performed by virtually anyone with minimal training and plankton) that are suspended in lake water influence trans-
inexpensive equipment. parency. These living aquatic communities undergo seasonal
and annual growth cycles, resulting in changes in their over-
all density, and in their location in the water column.
Secchi transparency is often at a low point soon after the
ice melts in the spring. That is when lakes mix, or "turn
Penetration
Light
over," causing nutrients and sediments from the lake
bottom to become suspended in the water for a period
of time.
Silica that is swept up from the bottom sediments stimu-
lates the growth of diatoms, a type of algae that experiences
In turbid lakes with In clear lakes with
peak growth in the spring and fall (see diagram below).
high algal density, light low algal density, light Diatom "blooms" often result in a brief period of reduced
penetration is limited, penetrates deeper, transparency in lakes. As the water warms and stabilizes
resulting in lower clarity resulting in greater clarity during the summer, other types of algae will dominate the
and measurably shallower and measurably deeper water column, depending on water temperature, nutrient
Secchi disk readings. Secchi disk readings. levels and other factors. Some lakes become progressively
less clear through the summer months, while others may
Secchi disk transparency is an indirect water quality become clearer. The concentration of phosphorus in the
indicator, because an assumption is made that water clar- water, the shape and depth of the lake basin, the orienta-
ity is affected primarily by algal growth in the water. tion of the basin to prevailing winds, and the weather all
That assumption is reason- influence water clarity, or transparency. Individual lakes are
able in most cases. However, unique in the way that they respond to these influences.
other factors may influence
transparency, including the
amount of sediment that is
suspended in the water, and
natural water color.
Natural color and suspended
sediments vary widely from
one lake to another. Color
is influenced by the concen-
tration of natural dissolved
Secchi Transparency organic substances in the
The distance one can see into the
water column is measured with water. These "humic acids"
a viewing scope and a Secchi disk can stain the water in some
attached to a calibrated line.
lakes to the point where light image courtesy of waterontheweb.org
Water Quality Volunteer lake water quality monitors learn over time what The following graphics illustrate the variability in Secchi
is "normal" for the lake that they monitor. transparency readings that may occur in lakes during a
single season, and from year to year. Figure 1 shows the
Many Secchi transparency readings are needed over a variation in annual Secchi transparency over a period of
period of years in order to confidently detect and track years in Annabessacook Lake, Kennebec County, and
trends in lake water quality. The natural variability of Cold Rain Pond, Cumberland County. Figure 2 shows
water clarity and other indicators of lake quality compli- the seasonal Secchi transparency variation in both lakes for
cates the detection of trends, which is why many complete the 2012 season.
seasons of data are generally needed in order to be able to
recognize a true change in water quality. Thus volunteers
are asked to collect complete seasons of data from May
through September—or later—each year.
Comparison of Secchi Transparency Variation in Two Maine Lakes
Figure 1 Figure 2
Annual Variation in Lake Water Clarity Seasonal Variation in Lake Water Clarity
(Secchi Transparency) for Two Lakes (Secchi Transparency) for Two Lakes
Annabessacook Lake Annabessacook Lake
Cold Rain Pond Cold Rain Pond
Figure 1 shows the annual average Secchi transparency readings Figure 2 shows the variation of Secchi transparency readings in a
for two Maine lakes. The minimum and maximum readings for single season for two Maine lakes. In 2012 the Secchi Transparency
each year are indicated by the bars above and below the disk which in Annabessacook Lake varied from a low reading of 1.4 meters in
indicates the average. The graph for Annabessacook Lake shows October to a high of 6.3 meters in August, with an average for the
the annual average Secchi transparency to range from 2.0 to 4.9 season of 4.0 meters. During the same year Cold Rain Pond varied
meters over a 37-year period. The graph for Cold Rain Pond shows from 2.9 meters in August to 5.6 meters in May with an average of
a smaller range from 3.9 to 5.3 meters over a 25-year period. 3.9 meters. In a single season Secchi transparency may vary only one
Annual variation in Secchi transparency is, for the most part, the or two meters, such as in Cold Rain Pond, or it may vary by several
result of seasonal changes in the composition, density and location meters, as in the case of Annabessacook Lake.
of algal populations in lakes. Both natural (weather) and human In most lakes if only one or two Secchi disk readings were taken
(watershed development) factors influence this process, requiring during the year, a misleading picture of the overall transparency
a minimum of 10 years of data to confidently detect trends in could emerge, depending on the timing of the readings during
water clarity. the summer.
Water QualityMonitoring Dissolved Oxygen and Some oxygen loss occurs naturally during the summer
months as water temperatures rise, because the solubility
Lake Water Temperature of oxygen in water is inversely proportional to the water
Another critical indicator of the health and quality of lakes temperature. In other words, cold water is able to contain
and ponds is the concentration of oxygen that is dissolved more oxygen than warm water (all other factors being
in the water. Dissolved oxygen (DO) levels in lake water held equal.) However, as lakes become more biologically
are influenced by many factors, including water tempera- productive, and organic matter accumulates in the sys-
ture, the concentration of algae and other plants in the tem, the potential increases for oxygen levels to decline as
water, and the amount of nutrients and organic matter the organic matter decomposes in deep, stratified areas.
that flow into the water body from the watershed. Oxygen Oxygen depression or depletion can stress fish and other
is produced through plant metabolism (photosynthesis), aquatic biota, and under certain circumstances, it can
and it is consumed during respiration and decomposition. cause an acceleration in the decline of water quality.
Oxygen in lake water is also influenced by wind and wave
action through weather events and the exposure of surface
water to atmospheric sources.
An adequate supply of dissolved oxygen in lake water is
essential to fish and other aquatic life forms. DO is also a
sensitive indicator of change in water quality, and of the
ability of a water body to support aquatic life. The loss,
over time, of DO in the deep areas of a lake, especially
during summer months, may indicate that the ecosystem
is stressed and changing.
Biological activity peaks in lakes and ponds during the
warm weather months. It is also at this time that the phe-
nomenon of thermal stratification (see Figure 3) occurs.
The combined influence of the two processes has a pro-
nounced effect on water chemistry, and in particular on
dissolved oxygen levels. The physical isolation of deep,
cold water at the bottom of a lake from the surface water Volunteers take a temperature and DO profile at a VLMP training workshop.
during summer stratification prevents the oxygen supply
in the deeper water from being replenished. The period Volunteer monitors are trained to measure oxygen con-
of isolation varies from one body of water to another, centrations in the water using inexpensive chemical kits
and depends on depth, and the influences of weather. and a simple sampling device. This method is accurate
Stratification may last from several weeks to a few months and reliable, although somewhat time-consuming. The
and it may exist only during warm, calm periods in shal- temperature of the water must also be recorded for each
lower waterbodies. oxygen reading. A more costly, but time-saving alternative
Figure 3 involves the use of a probe that is attached to an oxygen
meter via a cable. The probe and meter simultaneously
measure dissolved oxygen and water temperature, and the
information is displayed on the meter.
Oxygen concentrations and water temperature are gener-
ally recorded throughout the summer stratification period,
from early spring through late summer and early fall, when
DO levels are likely to be lowest in Maine lakes and ponds.
Based on University of
Wisconsin Extension image Readings are generally taken from the water surface to the
bottom of the deepest area of a lake, at one-meter inter-
Thermal Stratification
As lake water is warmed in the summer, in deeper lakes, three vals (depending on the individual water body.) Dissolved
distinct temperature layers form: oxygen is measured in milligrams per liter (mg/L) or parts
1) warmer (less dense) epilimnion layer at
the surface
per million (ppm).
2) the thin thermocline (transition) layer
3) the cold and deep hypolimnion layer
Water Quality Figure 4 illustrates the influence of seasonal Figure 4 Effects of Thermal Stratification on Dissolved Oxygen
thermal stratification on water temperature Concentrations in Oligotrophic and Eutrophic Lakes
and dissolved oxygen concentrations in lakes
with both high and low biological produc-
tivity. Oligotrophic lakes have low concen-
trations of phosphorus and algae, and deep
Secchi disk readings, whereas eutrophic lakes
have high concentrations of phosphorus and
algae and shallower Secchi disk readings.
Spring turnover occurs shortly after “ice-
out.” Spring winds cause the lake water
column to mix thoroughly, resulting in
uniform temperature and oxygen concentra-
tions from the surface to the bottom of the
lake, as shown in the graph on the far left.
During summer stratification, temperature
profiles are similar for both oligotrophic Image from Water on the Web
and eutrophic lakes, showing uniform www.WaterOntheWeb.org T = Temperature in Celsius DO = Dissolved Oxygen in mg/L
temperature near the surface to several
meters depth (epilimnion). Water temperature drops Monitoring Total Phosphorus
rapidly through the thermocline, then stabilizes in the
deepest area of both lakes (hypolimnion). The temperature
Concentrations in Lakes
gradient from the surface to the bottom of the lake can Volunteer monitors are trained to collect total phosphorus
be as much as twenty degrees in deep lakes. However, samples from their lakes, using a simple process of obtain-
in oligotrophic lakes dissolved oxygen levels rise as the ing a sample from a few inches below the water surface
water temperature drops in the thermocline, whereas in at the designated monitoring station. Total phosphorus
eutrophic lakes, oxygen levels drop, resulting from the analysis includes both organic and inorganic forms of the
decomposition of organic matter in the lake. element that may be present in the water, in solution or in
particulate form.
Shorter days and cool weather in the fall cause the water
temperature to drop to the point where the water column Phosphorus is the nutrient that most influences the
mixes, resulting once again in near uniform temperature growth of algae in lakes. An increase in the concentra-
from the surface to the bottom. The mixing process intro- tion of total phosphorus in lake water generally indicates
duces oxygen from the atmosphere into the water, resulting a potential increase in biological productivity (trophic
in uniform, high concentrations of dissolved oxygen for
both lake types. Figure 5
Pennesseewassee Lake
During winter stratification, water temperature profiles 2007 Monthly Total Phosphorus
are once again similar for both lake types. Ice on the lake Concentrations
surface causes the surface temperature to be slightly lower
than in the deep water below. The temperature gradient
from the surface to the bottom is relatively small, usually
Total Phosphorus (ppb)
only a few degrees. The oligotrophic lake retains high
concentrations of dissolved oxygen from the surface to the
bottom of the lake, but highly productive eutrophic lakes
may be depleted of oxygen.
The two examples illustrated represent opposite ends of the
lake productivity continuum. Every lake is unique, resulting
in many variations in both the temperature and oxygen
regimes that may be encountered throughout the year.
10 Water Qualitystate) of the system. Tracking in-lake phosphorus levels the season. However, if a single sample for the season was
over time is another way of monitoring changes in lake taken in June, the concentration of that sample (12 ppb)
water quality. Combined with Secchi transparency read- would suggest much more phosphorus-based productivity
ings, TP data provides additional information about lake in the lake for the summer.
ecosystem dynamics.
Ideally, phosphorus samples should be taken from early
Advanced Lake Monitoring
summer through the end of the sampling season in Accurate lake water quality characterization requires that
September or October. However, the sample analysis periodic "baseline" data be collected for all of the lakes in
involves laboratory fees, and volunteers are often limited to the VLMP. Maine DEP and VLMP staff strive to collect
taking one or two samples during the late summer (about additional water quality data for all lakes in the program,
mid-August), when biological activity is at a peak. The and for other lakes and ponds with special concerns. This
VLMP arranges to provide volunteer monitors with special is done on a rotating basis, and as financial resources allow.
sampling and laboratory mailing containers to facilitate Baseline sampling of program lakes occurs approximately
the collection of phosphorus data. every three to five years during the late summer. Volunteers
who wish to assist in obtaining advanced baseline samples
As is the case with most indicators of lake water qual-
from their lakes may participate in special workshops
ity, the concentration of phosphorus in lake water varies
offered by VLMP and DEP staff. This additional informa-
within individual seasons, and from one year to the next.
tion adds considerable value to data collected by volunteer
Therefore it is important to collect multiple samples
monitors. Using sample methods such as those in Table 1,
during the monitoring season, when possible. Figure 5
baseline data are gathered for the following indicators of
illustrates an example of the variation in total phosphorus
lake water quality:
samples (measured in parts per billion- ppb) from a Maine
lake over the course of the five month monitoring season. • Total Phosphorus • Total Alkalinity
The average total phosphorus concentration in this lake • Chlorophyll a • Phytoplankton
• True and Apparent Color • Anions and Cations
for the five month period is 9 ppb, which just happens to
• Conductivity • Zooplankton
be within 1 ppb of four of the five monthly samples taken.
• pH
If a single sample was taken in the month of August, which
is the optimum time for a single phosphorus sample taken For an explanation of these indicators of lake water quality,
during a five month monitoring season, the concentration please see Appendix A on page 30.
of that sample (7 ppb) would be close to the average for
Table 1 Examples of Water Sampling Methods
Surface Grab Epilimnetic core Profile Grab
Water is collected from just below the lake Using special weighted plastic tubing, an A discrete sample is taken at a specific depth
surface, using a special sampling bottle. integrated (mixed) water column sample is in the water column, using a device designed
taken from the upper temperature stratum to “grab” a sample at that depth.
of the lake where most algae growth takes
place. Epilimnetic core samples are taken to Bottom Grab
determine the average concentration in the A discrete sample is taken one meter
water column for a number of variables. from the bottom of the lake using a grab
sampling device.
Water Quality 112012 Water Quality Monitoring For lakes in which the majority of phosphorus is from the
watershed, it is reasonable to speculate that reduced storm-
Season in Review water runoff during the spring and summer, when Maine
lakes are the most biologically productive, is likely to result in
Influences on Lake Water Quality lower concentrations of sediment and nutrients being trans-
Weather often plays a significant role in the seasonal and ported to the water from the watershed, resulting in less food
annual variability of lake data. The indicators that are used for algae, fewer sediment particles in the water, and deeper
to assess lake water quality can vary significantly as a result Secchi disk readings.
of the timing, intensity and duration of precipitation, wind,
Figure 6
cloud cover, and air/water temperatures.. Volunteer lake Comparison of 2012 water clarity of 415 Maine lakes
monitors help take these influences into account by record- to their long-term clarity.
ing weather data on lake survey forms, especially notable
local events, such as heavy rain and periods of sustained Table 2
strong wind. Deviation Number of
(meters) Lakes
Human activity also influences lake water quality. -1.6 or less 5
Development in lake watersheds causes changes in the 39.5% -1.1 to -1.5 10
quantity and quality of stormwater runoff to lakes and More Clear
49.6%
-0.6 to -1.0 58
-0.1 to -0.5 133
ponds. Runoff is the vehicle that carries pollutants such as Less Clear
Zero 45
phosphorus and sediment through watersheds into lakes. 0.1 to 0.5 115
Weather has an obvious bearing on this process, as well. 0.6 to 1.0 33
Separating and understanding natural watershed influences 10.8%
1.1 to 1.5
1.6 to 2.0
14
0
from those associated with human activity, and identifying No Change
2.1 or more 2
true changes in lake water quality over time, is a challenging
undertaking, to say the least! Note: Consideration was not given to whether or not some Secchi disk
In a typical annual cycle, a high percentage of the annual readings hit bottom, or whether 2012 was the first year for which data
were gathered on a small number of lakes.
phosphorus loading to lakes from their watersheds is likely
to occur during the spring runoff period. When spring and
early summer stormwater runoff is above or below normal, 2012 Weather Influences on Maine Lakes
we might expect that there would be more or less algae Maine weather during the winter, spring and summer of
growth during the summer months, resulting in reduced or 2012 was unusual, and could be characterized as “extreme.”
improved water clarity for a majority, but not all, lakes. Precipitation during the winter and spring throughout
Each lake (and its watershed) has unique characteristics that much of Maine was light, resulting in a lower than nor-
cause it to respond in a particular way to human and natu- mal snowpack and spring runoff. The weather was also
ral influences. The shape, depth, and size of the lake basin, abnormally warm throughout much of the winter, and
the topography, hydrology and geochemistry of the water- especially in March, when air temperatures exceeded 80
shed, the orientation of the basin to prevailing winds, and degrees F. in southern and central areas of the state. Lake
other natural factors, account for some of the seasonal and ice melted rapidly, and most lakes throughout Maine were
annual “natural variation” that is observed in lake systems. free of ice from 3-4 weeks earlier than their historical
While some lakes may be clearer during periods of reduced average. National Weather Service records indicate that
precipitation, perhaps because there is less phosphorus Portland experienced the 2nd warmest April in 72 years,
and sediment-laden stormwater runoff flowing into them and May was the 9th consecutive month during which the
during such times, others may not show the same posi- temperature was above normal. While June temperatures
tive response because they already support moderate algae were closer to normal, July 2012 was the warmest (July) on
growth and experience late summer dissolved oxygen loss. record, and Portland experienced the 5th warmest August
For this latter set of lakes, wind levels during the summer in 72 years. Precipitation was above normal in May, June,
months may play an important role in whether or not phos- July and August.
phorus from bottom sediments becomes available to algae The early loss of ice cover, combined with very warm air
near the surface, a phenomenon called internal recycling. temperatures caused thermal stratification to occur earlier
Phosphorus in sediments is generally either bound weakly than normal in the spring. On June 3 an intense rain event
to iron or more permanently to aluminum. When dissolved occurred, during which areas of southern and central Maine
oxygen is depleted, iron can release its phosphorus to the received from 6 to 8 several inches of precipitation in just
waters above and heavy winds may circulate the water such over 24 hours. Many volunteer monitors reported observa-
that the phosphorus gets recycled to the surface waters tions of severe soil erosion from stormwater runoff in their
becoming available to support algal growth. lake watersheds, often resulting in dramatic drops in Secchi
12 Water Qualitytransparency. For example, early season Secchi readings on Figure 7
Thompson Lake in Oxford were in the 9 meter range, but Yearly Comparison of Lakes that were Clearer, Less
following the June storm, the Secchi reading dropped to 5.3 Clear, or the Same as their Long-Term Annual Average
meters. Similarly, in Lake Auburn, only a few days before
the storm, the Secchi reading was 7.3 meters, but water clar-
ity dropped to 5.6 meters following the storm. Continued
abnormally warm weather resulted in lake surface tempera-
tures in southern and central Maine reaching, and in some
Percentage of Lakes
cases excedeing 80 degrees F. by the end of June.
Maine lakes as a whole, were less clear in 2012 than in
2011 and 2010, as Figure 8 illustrates. The annual average
Secchi transparency for all lakes monitored throughout the
State was 5.21 meters. In addition to the continued drop in
overall lake clarity in 2012, fewer individual lakes were as
clear as they have been historically, compared to 2011 and
2010, as the following summary details.
Year
2012 Secchi Transparency (Water Clarity),
and compare this to previous years (Figure 8). For example,
Compared to Historical Data in 2003, the statewide Secchi transparency average was one
The VLMP and Maine DEP compared the 2012 average of the highest on record at 5.75 meters. But reduced water
Secchi disk values for 415 Maine lakes to their long-term clarity for a larger number of lakes in 2004 lowered the aver-
(historical) average Secchi values. Within that group, 164 age to 5.39 meters. In 2005, the average dropped to 5.26
lakes (39.5%) were clearer, 45 (10.8%) were the same as meters and in 2006, statewide Secchi transparency dropped
their historical average, and 206 lakes (49.6%) were less to 5.1 meters, the lowest annual average in seven years. In
clear (Figure 6). Deviations from the average in both 2007, Maine lakes rebounded to 5.65 meters—the fourth
directions (plus and minus) varied from as little as a tenth clearest year for Maine lakes since 1974. But the following
of a meter to nearly two meters. Table 2 lists the ranges year, the average dropped to 5.34 meters, which may come
of clarity deviation for the set of lakes that were compared as no surprise, considering that lakes that were monitored
in 2012. in 2008 were more or less evenly split between those that
were clearer than, and less clear than they had been histori-
Figure 7 illustrates the variation described above during the
cally. The average continued to fall to 5.14 meters in 2009,
past decade. Compared to the past decade, 2012 was one
following two extremely wet years in the State of Maine. In
of the least clear years for many Maine lakes, in that nearly
2010, the statewide Secchi average increased to 5.6 meters,
half of the lakes monitored were less clear than their histori-
one of the two clearest years for Maine lakes in the past
cal average. This percentage was only matched or exceeded
seven years, but in 2011 – a much “wetter” year than 2010,
during two other years (2006 and 2011) since 2001.
the average dropped to 5.33 meters. In 2012, the average
Another way to consider conditions monitored in 2012 is continued to drop to 5.21 meters, one of a few low statewide
to determine the average of all of the individual lake annual averages in the past decade.
Secchi averages for a given year (average of all the averages),
Figure 8 Annual Secchi Transparency Averages for Maine Lakes
Figure 8 is a plot of the average annual Secchi
disk transparency for all Maine lakes for which
data have been available from 1970 through
Secchi Depth (meters)
2012. During the first few years of this period
the number of lakes on which the average is
based was relatively small. This may account
for the high degree of fluctuation up until
1975, when the number of lakes in the data
set exceeded 100. Since 1975, the number of
lakes used to determine the annual average
has increased steadily to more than 400
per year. The graph shows that for most
years after 1975 the statewide average has
been between 5.0 and 5.5 meters. The 2012
Year average was 5.21 meters.
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