Lyon County Lake Quality
Minnesota, 5 lakes, average grade F (Very Poor)
Lyon County has 5 graded 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. The county average is F — the most-stressed bracket in our rubric. Most monitored lakes here show persistent nutrient loading and algal pressure.
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. Island Lake (F) is the cleanest in the county.
Quick Answers for Lyon County
Planning a trip? Check special fishing regulations for Island Lake, whether the fish are safe to eat, and the best times to fish — or browse the full Minnesota regulations index.
DNR Reports (12)
Minnesota DNR LakeFinder resources for lakes in Lyon County. browse all reports →
- —Fisheries Lake Survey — School GroveFisheries Lake Survey · MN DNR LakeFinder
- —Fisheries Lake Survey — Lady SlipperFisheries Lake Survey · MN DNR LakeFinder
- —Fisheries Lake Survey — IslandFisheries Lake Survey · MN DNR LakeFinder
- —Fisheries Lake Survey — CottonwoodFisheries Lake Survey · MN DNR LakeFinder
- —Fish Stocking History — CottonwoodFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — CottonwoodPublic Water Access Sites · MN DNR LakeFinder
- —Fish Stocking History — IslandFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — IslandPublic Water Access Sites · MN DNR LakeFinder
- —Fish Stocking History — Lady SlipperFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — Lady SlipperPublic Water Access Sites · MN DNR LakeFinder
- —Fish Stocking History — School GroveFish Stocking History · MN DNR LakeFinder
- —Public Water Access Sites — School GrovePublic Water Access Sites · MN DNR LakeFinder
All Lakes in Lyon County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Island Lake | F | 2 ft | 8 ft | 123 µg/L |
| 2 | Cottonwood Lake | F | 1.8 ft | 7 ft | 186 µg/L |
| 3 | Lady Slipper Lake | F | 1.5 ft | 11 ft | - |
| 4 | School Grove Lake | F | 2 ft | 11 ft | - |
| 5 | Brown Marsh Lake | F | 1.6 ft | - | 98 µg/L |
Source: EPA National Aquatic Resource Surveys, 2026.