Pennsylvania Lake Water Quality

Pennsylvania lists 570 lakes across 65 counties, 83 of them with a recent water-quality reading. Most of that sampling flows through monitoring run by the Pennsylvania Department of 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. Most measured Pennsylvania lakes are productive, often shallow, and frequently algal in late summer; each lake page shows its own phosphorus and chlorophyll-a readings.

Pymatuning Reservoir is the largest lake in this index at about 13,926 acres, one of 30 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. Eutrophic conditions dominate the measured set: nutrient-loaded, productive, with algal pressure that shows up most years in late summer. These lakes tend to be shallow, in agricultural watersheds, and over-warmed by the time July ends. The county with the lowest nutrient and algae readings on average is Adams. The gap between counties is large enough that a single figure for Pennsylvania lake water quality hides real local variation.