North Dakota Lake Water Quality

139 of the 826 North Dakota lakes in this index carry a recent clarity, phosphorus or algae reading, spread over 51 counties. Those readings come from the North Dakota Department of Environmental Quality, 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. Most measured North Dakota lakes are productive, often shallow, and frequently algal in late summer; each lake page shows its own phosphorus and chlorophyll-a readings.

By surface area the largest lake here is Lake Audubon, at about 19,095 acres, and 132 of the lakes in this index cover more than 500 acres. Size is worth knowing before you go: a large deep basin buffers nutrient inputs by sheer volume, while a shallow one warms quickly and can turn over its whole water column in a single summer storm. 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 Rolette. The gap between counties is large enough that a single figure for North Dakota lake water quality hides real local variation.