Connecticut Lake Water Quality

Connecticut lists 379 lakes across 17 counties, 90 of them with a recent water-quality reading. Most of that sampling 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. The remainder are here because they are real named lakes, not because anyone has sampled them recently. Low nutrient readings are less common among Connecticut's measured lakes. The smaller, agricultural-watershed lakes that dominate the measured set tend to carry persistent phosphorus loads.

Lake Candlewood is the largest lake in this index at about 5,600 acres, one of 11 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. Most measured Connecticut lakes sit in the mesotrophic band: moderate productivity, decent clarity, capable of supporting both warm-water and cool-water fisheries. This is the band where well-managed working lakes tend to land. Tolland has the lowest nutrient and algae readings on average. With only 17 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.