Vermont Lake Water Quality

111 of the 308 Vermont lakes in this index carry an A–F water-quality grade, spread over 14 counties. Those grades rest on measurements from the Vermont Department of Environmental Conservation, alongside federal programs and volunteer monitoring networks. The rest are listed for their size, depth and location, without enough recent nutrient or algae sampling behind them to support a letter. About 61% of graded Vermont lakes pull an A, 68 top-bracket waters. That high A-share comes mostly from the cold, deep, kettle-formed lakes in the north of the state, which buffer themselves against nutrient inputs.

Lake Bomoseen is the largest lake in this index at about 2,360 acres, one of 19 here that clear 500 acres. The rest run smaller, and small and shallow is where nutrient loading shows up first, because there is less water to dilute it and the bottom sediment stays within reach of the sun. Mesotrophic is the dominant trophic class among the graded lakes, a workable middle ground between the pristine oligotrophic deep lakes and the algal-pressured eutrophic shallow ones. Orange ranks highest on average county grade (A), and Franklin sits lowest. With only 14 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.