How are these rankings calculated?

Lakes are graded A through F on nutrients and algae — total phosphorus, nitrogen, chlorophyll-a, and turbidity — against EPA National Lakes Assessment 2022 condition classes for that lake’s ecoregion. Water clarity (Secchi depth) is measured and shown; it is not the letter. Lakes without enough recent samples are UNRATED, not given an F. Source data comes from the EPA Water Quality Portal.

Safest Lakes to Swim In in South Dakota

There is not enough monitoring data to rank swimming safety in South Dakota. That is a gap in the data, not a verdict on these lakes. Check state and county advisories before you swim.

More Answers for South Dakota