Wyoming Lake Water Quality

Wyoming lists 731 lakes across 21 counties, 164 of them with a recent water-quality reading. Most of that sampling flows through monitoring run by the Wyoming Department of Environmental Quality, 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 Wyoming lakes are productive, often shallow, and frequently algal in late summer; each lake page shows its own phosphorus and chlorophyll-a readings.

Glendo Reservoir Lacustrine Littoral is the largest lake in this index at about 23,320 acres, one of 48 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 measured lakes, a workable middle ground between the pristine oligotrophic deep lakes and the algal-pressured eutrophic shallow ones. Johnson has the lowest nutrient and algae readings on average. With only 21 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.