Unknown County Lake Quality
Minnesota, 5 lakes, average grade B (Good)
Only 5 lakes in Unknown County carry an active grade. The county-level summary is therefore representative of those specific lakes, not necessarily of every water body in the county. The county-wide average lands at B — solid water quality with most lakes carrying clear summer transparency and low-to-moderate phosphorus.
Many of the county's lakes are deep glacial basins — over 50 feet at their deepest point — which gives them thermal stratification and a buffer against summer warming. Birch Lake (grade A) is the cleanest in the county.
Quick Answers for Unknown County
Planning a trip? Check special fishing regulations for Birch Lake, whether the fish are safe to eat, and the best times to fish — or browse the full Minnesota regulations index.
DNR Reports (6)
Minnesota DNR LakeFinder resources for lakes in Unknown County. browse all reports →
- —Fisheries Lake Survey — AshdickFisheries Lake Survey · MN DNR LakeFinder
- —Fisheries Lake Survey — OttertrackFisheries Lake Survey · MN DNR LakeFinder
- —Fisheries Lake Survey — ClearwaterFisheries Lake Survey · MN DNR LakeFinder
- —Fisheries Lake Survey — BirchFisheries Lake Survey · MN DNR LakeFinder
- —Aquatic Plant Report — Clearwater (1828)Aquatic Plant Report · MN DNR LakeFinder
- —Public Water Access Sites — ClearwaterPublic Water Access Sites · MN DNR LakeFinder
All Lakes in Unknown County
| Rank | Lake | Grade | Clarity | Max Depth | Phosphorus |
|---|---|---|---|---|---|
| 1 | Birch Lake | A | 15 ft | 34 ft | - |
| 2 | Swamp Lake | A | 16.2 ft | 50 ft | - |
| 3 | Mountain Lake | A | 19 ft | 130 ft | - |
| 4 | Carp Lake | C | 8.5 ft | 34 ft | - |
| 5 | Seed Lake | C | 7 ft | - | - |
Other Counties in Minnesota
See how Unknown County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 12 states.
Source: EPA National Aquatic Resource Surveys, 2026.