Walworth County Lake Quality
South Dakota, 4 lakes — no lake here has enough monitoring data for a grade
Walworth County has 4 monitored lakes — a thin enough sample that one or two stressed lakes can move the county average noticeably. Use the per-lake pages below for what actually matters. No lake in Walworth County has enough sampling behind it for an A–F grade yet. The 4 monitored lakes below carry whatever clarity, phosphorus, and chlorophyll-a measurements exist.
Most of the county's monitored lakes are shallow, under 50 feet, which means wind keeps the water column mixed all summer and sediment-bound phosphorus releases back into the surface layer whenever the bottom is disturbed.
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Quick Answers for Walworth County
Planning a trip? Check special fishing regulations for Swan Lake — or check the official South Dakota fishing regulations.
All Lakes in Walworth County
4 lakes · 0 graded, 4 not rated0 graded lakes · 4 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| NRSwan LakeWalworth | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRMolstad LakeWalworth | NR | No recent samples | No recent samples | No recent samples | No recent samples | ✓ Public | |
| NRSpring LakeWalworth | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRHorseshoe LakeWalworth | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded |
NR = not rated: there is not enough recent sampling to support a letter. That is EPA Integrated Reporting Category 3 (insufficient information), not a failing grade. How grading works.
Lake Match
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Other Counties in South Dakota
See how Walworth County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all United States (49 states), Canada (Ontario, Québec, Nova Scotia, British Columbia and Newfoundland and Labrador), and 38 other country hubs..
Source: EPA National Aquatic Resource Surveys, 2026.