Connecticut Lake Water Quality

94 Connecticut lakes carry a grade. Most of the input data flows through monitoring run by the Connecticut Department of Energy and Environmental Protection, which feeds state, federal, and volunteer measurements into the EPA Water Quality Portal. Only about 0% of Connecticut's lakes pull an A grade — the smaller, agricultural-watershed lakes that dominate the dataset tend to carry persistent nutrient loads. 11% of lakes fall in the D or F brackets.

Mesotrophic is the dominant trophic class — a workable middle ground between the pristine oligotrophic deep lakes and the algal-pressured eutrophic shallow ones. Tolland ranks highest on average county grade (B). Hartford sits lowest. With only 8 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.