Document Type


Study Date



In the summer and fall of 2009, the Colby Environmental Assessment Team (CEAT) studied the water quality of Salmon Lake and McGrath Pond, located in the Belgrade Lakes Region of Maine. The physical, chemical and biological characteristics of water quality were measured and analyzed to evaluate the current health of these lakes. Water quality data collected during the summer and fall of 2009 were compared with data from previous years to study the historic water quality trends. Land use patterns in the Salmon/McGrath watershed were also examined to investigate their impact on the lake water quality. The water quality trends suggest an improvement in the transparency of Salmon Lake and McGrath Pond over the last 34 years. Improvements in transparency have been greater for McGrath Pond than for Salmon Lake. In 1975, McGrath Pond and Salmon Lake had transparencies of 4 m and 5 m, respectively. In 2009, both water bodies had transparencies of approximately 5.5 m. Data from 2009 show the productivity of Salmon Lake to be higher. Consequently the threat of eutrophication is higher in Salmon Lake than in McGrath Pond. Mean phosphorus levels recorded in this study were 13 ppb for Salmon Lake and 10.6 ppb for McGrath Pond. In September of 2009, phosphorus levels at the deepest part of Salmon Lake approached 300 ppb compared to less than 10 ppb for McGrath Pond. Phosphorus from the bottom can be mixed into the water column during spring and fall mixing events. When phosphorus levels exceed 12-15 ppb, the lake is at risk for algal blooms. The last recorded algae bloom in Salmon Lake was in 2002-2003.


Publication Date: Spring 2010

Date of Study: Summer and Fall 2009



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