Cass Lake
Beltrami County, MinnesotaOligotrophic
Cass Lake is a cold, clear oligotrophic lake in Beltrami County, Minnesota. Water quality is graded A based on 2 sampling years through 2025. The lake supports 1 documented fish species including black bullhead,black crappie,bluegill,bowfin (dogfish),brown bullhead,burbot,greater redhorse,hybrid sunfish,lake whitefish,largemouth bass,muskellunge,northern pike,pumpkinseed,redhorse,rock bass,shorthead redhorse,tullibee (cisco),walleye,white sucker,yellow bullhead,yellow perch. Compared to the 91 other monitored lakes in Beltrami County, Cass Lake ranks #18 for water quality.
Source: EPA Water Quality Portal sampling records, Minnesota DNR LakeFinder, last sampled 2025-10-15. Grade methodology: LakeGrade methodology.
Swimming Safety
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A, Excellent
Crystal clear, you can see 18.5 ft down. Chlorophyll-a: 3.2 µg/L. Trophic State Index: 39.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 18.5 ft | A |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 3.2 µg/L | A |
| Trophic State Index (TSI) | 39 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Fish Species
Click a species to see all Minnesota and Wisconsin lakes where it is found.
→ Best fishing times for Cass Lake (14-day solunar calendar)
→ Is it safe to eat fish from Cass Lake? (mercury & PFAS guide)
→ Cass Lake fishing regulations (limits, seasons, special rules)
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
Ice Season
Historical ice data from Minnesota DNR (16 observations).
Estimated open water season: 224 days
| Earliest | Latest | |
|---|---|---|
| Ice-Out | 2021-04-06 (2021) | 2008-05-12 (2008) |
| Ice-In | 2008-11-24 (2008) | 2024-01-07 (2024) |
Most recent ice-out: 2025-04-27
Location
County Ranking
Ranked #18 of 92 lakes in Beltrami County
Nearby Lakes in Beltrami County
More Minnesota Lake Rankings
State Parks Near Cass Lake
Other Grade A Lakes in Minnesota
Oligotrophic Lakes in Minnesota
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Ice data from Minnesota DNR Climate
Most recent sample: 2025-10-15
Monitoring stations: 1