Colorado Lake Water Quality

101 of the 733 Colorado lakes in this index carry a recent clarity, phosphorus or algae reading, spread over 62 counties. Those readings come from the Water Quality Control Division of the Colorado Department of Public Health and Environment, 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. Measured Colorado lakes sit mostly in the middle of the nutrient range, with the highest phosphorus and algae readings in counties where row-crop agriculture dominates the watershed.

John Martin Reservoir is the largest lake in this index at about 11,590 acres, one of 79 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. The county with the lowest nutrient and algae readings on average is Pueblo. The gap between counties is large enough that a single figure for Colorado lake water quality hides real local variation.