Section 319
NONPOINT SOORCE PROGRAM SUCCESS STORY
Cobbossee Lake Restored: 35 Years of Sustained Work Succeeds
ImnrOVPd
Cobbossee Lake had a long history of nuisance algae blooms that
turned its once sparkling clear, trout-filled water murky green.
Nonpoint source pollution in Cobbossee Lake's watershed, as well as pollution from upstream lakes,
delivered excess phosphorus into the lake. Elevated phosphorus levels promoted algae blooms,
which discouraged recreation, spoiled aquatic habitat, and caused the lake to not meet water quality
standards. After 35 years of restoration work, including upstream alum treatments and widespread
installation of best management practices (BMPs), Cobbossee Lake exhibits remarkably improved
water clarity. The lake has been free of nuisance algae blooms for the past 10 years and now attains
water quality standards. This impressive recovery prompted the Maine Department of Environmental
Protection (DEP) to remove Cobbossee Lake from Maine's section 303(d) impaired waters list in 2006.
Problem
Cobbossee Lake (short for Cobbosseecontee), a
large 5238-acre lake in central Maine, is valued
by people for fishing, swimming, boating, and
wildlife. One of Maine's premier bass fishing
lakes, Cobbossee Lake is also a secondary source
of drinking water for Maine's capital — Augusta.
In the 1960s water quality in Cobbossee Lake
began to deteriorate. Elevated nutrient (i.e.,
phosphorus) levels spurred the growth of noxious
blue-green algae, which reduced water clar-
ity, formed green surface scums, and depleted
oxygen in the bottom waters of the lake. The
excess phosphorus in Cobbossee Lake's water-
shed was caused by soil erosion and runoff from
agricultural, residential, and commercial lands,
and the gradual conversion of forested land into
developed land. The other significant source of
phosphorus came from Annabessacook Lake,
immediately upstream of Cobbossee. At one
time, Annabessacook received sewage dis-
charges from the town of Winthrop, and this nutri-
ent-rich sewage caused algae blooms. Although
sewage discharges to Annabessacook Lake were
eliminated by 1977, the phosphorus in the lake's
sediments continued to recycle and flow into
Cobbossee Lake.
The Total Maximum Daily Load (TMDL) assess-
ment developed for Cobbossee Lake in 1995
Governor Baldacci (left) and DEP Commissioner Littell (right) recognize
cleanup of Cobbossee Lake
estimated that two-thirds of the external phospho-
rus load came from the lake's direct 32-square-mile
watershed, and one-third came from the indirect
upstream watershed. Agriculture accounted for
about 60 percent of the phosphorus and developed
lands accounted for about 40 percent of the phos-
phorus load. The TMDL showed that in-lake phos-
phorus needed to be reduced to 15 parts per billion
(ppb), or 5,904 kg P/yr, for Cobbossee to attain
Maine's water quality criterion for water clarity
(more than 2 meters of Secchi Disc Transparency).
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76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06
YEAR
Minimum Secchi Depth read-
ings (1976-2006) indicate no
nuisance algal blooms have
occurred since 1997. Maine's
definition of a nuisance algae
bloom is a minimum Secchi Disc
Transparency of less than 2.0
meters in lakes.
Project Highlights
Cobbossee Watershed District (CWD), formed
in 1973, collaborated with nine municipalities,
Maine DEP, and federal agencies to restore
Cobbossee Lake. In the 1970s and 80s, funding
from EPA's Clean Lakes Program and United States
Department of Agriculture's (USDA) Farm Bill
Program helped farmers reduce polluted runoff on
31 dairy farms. Other farmers in this area received
technical support from Maine DEP and USDA.
EPA funded two alum treatments that contributed
to Cobbossee Lake's recovery. Alum forms an alu-
minum hydroxide precipitate that removes phospho-
rus from the water column and forms a long-lasting
barrier on the lake bottom that substantially reduces
phosphorus released from sediment. In 1978, CWD
conducted an alum treatment in Annabessacook
Lake. In 1986, an alum treatment and watershed
BMP-implementation at another upstream lake,
Cochnewagon, further reduced phosphorus inputs
to Cobbossee Lake.
In addition, CWD helped towns and landowners
adopt erosion control BMPs at homes, on town
roads, and on private camp roads. In the early
1990s, five towns adopted ordinances requiring
that new developments be designed to meet strict
phosphorus allocation standards for stormwater
runoff. Under two EPA section 319-funded projects
in the 1990s, a significant number of erosion control
and nutrient management practices were installed
on dairy farms, along roads, and on residential prop-
erties. One of these section 319 projects was in
Jock Stream, a major tributary responsible for one-
third of the phosphorus loading from Cobbossee
Lake's direct watershed.
Results
Cobbossee Lake now meets water quality stan-
dards, which in Maine means that the lake has a
stable or improving trophic state and has been free
of culturally induced algae blooms. Maine DEP
removed Cobbossee Lake from the state's 303(d)
list during the 2006 cycle.
Partners and Funding
CWD provided sustained leadership, water quality
assessment, and technical services. Many local,
state, and federal partners contributed funding
and services over the years. Key partners include
watershed towns, the Kennebec County Soil and
Water Conservation District (SWCD), USDA, Maine
DEP, EPA, Maine Department of Transportation,
Cobbossee Lake Association, Annabessacook
Lake Improvement Association, and Friends of
Cobbossee Watershed.
From 1975 to 1985, EPA provided more than $1 mil-
lion in Clean Lakes grants for diagnostic studies and
restoration activities, including alum treatments
and BMP installations, throughout the CWD. Two
EPA section 319-funded projects helped control
NPS in the watershed. From 1995 to 1998, CWD
demonstrated effective erosion and sediment
control BMPs using $35,820 in section 319 funds
and $23,880 in matching funds. From 1999 to 2004,
Kennebec County SWCD reduced phosphorus and
sediment export from roads and farms in the Jock
Stream watershed using $220,040 in section 319
funds and $152,117 in matching funds.
U.S. Environmental Protection Agency
Office of Water
Washington, DC
EPA841-F-07-001F
May 2007
For additional information, contact:
Norm Marcotte, Maine Department
of Environmental Protection
207-287-3901 • norm.g.marcotte@maine.gov
William Monagle, CLM, Cobbossee Watershed District
207-377-2234 • cwd@fairpoint.net
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