Indiana Lake Water Quality

143 of the 387 Indiana lakes in this index carry a recent clarity, phosphorus or algae reading, spread over 64 counties. Those readings come from the Indiana Department of Environmental Management, alongside federal programs and volunteer monitoring networks. The rest are listed for their size, depth and location, with no recent nutrient or algae sampling behind them. Low nutrient readings are less common among Indiana's measured lakes. The smaller, agricultural-watershed lakes that dominate the measured set tend to carry persistent phosphorus loads.

Brookville Lake is the largest lake in this index at about 4,364 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. Most measured Indiana 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. The county with the lowest nutrient and algae readings on average is Steuben. The gap between counties is large enough that a single figure for Indiana lake water quality hides real local variation.