Big Lake vs Cass Lake Allens Bay
Water quality, depth, fish species, and recreation comparison.
Big Lake and Cass Lake Allens Bay both received the same overall water quality grade of A (Excellent). Both are in Beltrami County, Minnesota.
Big Lake and Cass Lake Allens Bay are both in Minnesota — a same-state head-to-head where the comparison comes down to lake-specific differences in depth, watershed, and monitoring history rather than the broader state-level water-quality regime. These two are within a letter of each other on the rubric — Big Lake (A) versus Cass Lake Allens Bay (A). The deciding factors for a recreational visitor are likely physical (depth, access, fish species) rather than water-quality differences.
With grades 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 Allens Bay
Crystal clear, you can see 16.6 ft down.
Side-by-Side Metrics
| Metric | Big Lake | Cass Lake Allens Bay |
|---|---|---|
| Overall Grade | A (Excellent) | A (Excellent) |
| Water Clarity | 9.7 ft | 16.6 ft |
| Phosphorus | 15 µg/L | 18.5 µg/L |
| Chlorophyll-a (Algae) | 4.8 µg/L | 4.7 µg/L |
| Maximum Depth | 35 ft | 120 ft |
| Surface Area | 3,598 acres | 15,958 acres |
| Public Access | Yes | Yes |
| Fish Species | 17 | 21 |
| Trophic State | mesotrophic | mesotrophic |
Bold value = better for that metric (lower phosphorus / chlorophyll = cleaner; higher Secchi / depth / species count = better).
Verdict
Both lakes earn the same Grade A. The tiebreakers come down to clarity (Big Lake: 9.7 ft, Cass Lake Allens Bay: 16.6 ft) and what you want from the lake. Big Lake has fewer fish species than Cass Lake Allens Bay.
Source: EPA National Aquatic Resource Surveys, 2026.