Big Lake vs Cass Lake
Water quality, depth, fish species, and recreation comparison.
Big Lake and Cass Lake read the same on nutrients and algae. Both are in Beltrami County, Minnesota.
Both Big Lake and Cass Lake sit in Minnesota. A same-state comparison strips out the state-level water-quality regime as a variable: any differences in the readings here are about the lakes themselves, not the agencies sampling them. The readings are close: Big Lake and Cass Lake sit within a narrow band of each other on phosphorus, chlorophyll-a and clarity. The per-parameter table below shows where the small differences actually live.
With readings this close, the choice between the two lakes turns on non-water-quality factors: depth, fish species, public access, distance from home. The per-lake pages below cover all of those.
Big Lake
Moderate clarity, visible to about 9.7 ft.
Cass Lake
Crystal clear, you can see 18.5 ft down.
Side-by-Side Metrics
| Metric | Big Lake | Cass Lake |
|---|---|---|
| Water Clarity | 9.7 ft | 18.5 ft Better |
| Phosphorus | 15 µg/L | 11 µg/L Better |
| Chlorophyll-a (Algae) | 4.8 µg/L | 3.2 µg/L Better |
| Maximum Depth | 35 ft | 120 ft Better |
| Surface Area | 3,598 acres | 15,958 acres |
| Public Access | Yes | Yes |
| Fish Species | 17 | 21 Better |
| Trophic State | mesotrophic | oligotrophic |
A green ✓ marks the better value for that metric (lower phosphorus / chlorophyll = cleaner; higher Secchi / depth / species count = better). Surface area and trophic state carry no tick — a bigger lake is not a better lake.
Swap a lake
Compare Big Lake or Cass Lake against a different lake.
Verdict
Both lakes earn the same Grade A. The tiebreakers come down to clarity (Big Lake: 9.7 ft, Cass Lake: 18.5 ft) and what you want from the lake. Big Lake has fewer fish species than Cass Lake.
Source: EPA National Aquatic Resource Surveys, 2026.