Lyon County Lake Quality
Minnesota, 6 lakes, average grade D (Nutrient-rich)
Lyon County has 6 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-wide average grade is D — water quality issues are persistent across most of the monitored basins. 1 lakes fall into the F bracket outright.
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. Yankton Lake (D) is the cleanest in the county.
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Quick Answers for Lyon County
Planning a trip? Check special fishing regulations for Yankton Lake, whether the fish are safe to eat, and the best times to fish — or browse the full Minnesota regulations index.
Fishing in Lyon County
DNR Reports (12)
Minnesota DNR LakeFinder resources for lakes in Lyon County. browse all reports →
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —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
6 lakes · 2 graded, 4 not rated2 graded lakes · 4 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Max Depth | Access |
|---|---|---|---|---|---|---|---|---|
| 1 | DYankton LakeLyon | D | 0.8 ft | 98 µg/L | 20.3 µg/L | No recent samples | 8 ft | ✓ Public |
| 2 | FCottonwood LakeLyon | F | 1.8 ft | 154.5 µg/L | 64.5 µg/L | No recent samples | 7 ft | ✓ Public |
| NRIsland LakeLyon | NR | 2 ft | 123 µg/L | 46.8 µg/L | No recent samples | 8 ft | ✓ Public | |
| NRLady Slipper LakeLyon | NR | 1 ft | No recent samples | No recent samples | No recent samples | 11 ft | ✓ Public | |
| NRSchool Grove LakeLyon | NR | 1.5 ft | No recent samples | No recent samples | No recent samples | 11 ft | ✓ Public | |
| NRBrown Marsh LakeLyon | NR | 1.6 ft | 98 µg/L | 32.7 µg/L | No recent samples | No recent samples | ✓ Public |
NR = not rated: the monitoring record does not meet the evidence bar for a grade. That is EPA Integrated Reporting Category 3 (insufficient information), not a failing grade. How grading works.
Lake Match
Which lake suits how you actually use one?
Six questions — swimming, fishing, quiet, cabins, drive time — and a shortlist of graded lakes that fit, with the water quality behind each one.
Other Counties in Minnesota
See how Lyon County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 39 states and 2 Canadian provinces.
Source: EPA National Aquatic Resource Surveys, 2026.