Big Deep Lake vs Birch Lake
Water quality, depth, fish species, and recreation comparison.
Big Deep Lake and Birch Lake both received the same overall water quality grade of A (Excellent). Both are in Cass County, Minnesota.
Both Big Deep Lake and Birch Lake sit in Minnesota. A same-state comparison strips out the state-level water-quality regime as a variable: any grade differences here are about the lakes themselves, not the agencies grading them. These two are within a letter of each other on the rubric — Big Deep Lake (A) versus Birch Lake (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 Deep Lake
Crystal clear, you can see 19.4 ft down.
Birch Lake
Good clarity, visible to about 14 ft.
Side-by-Side Metrics
| Metric | Big Deep Lake | Birch Lake |
|---|---|---|
| Overall Grade | A (Excellent) | A (Excellent) |
| Water Clarity | 19.4 ft | 14 ft |
| Phosphorus | 7 µg/L | 12 µg/L |
| Chlorophyll-a (Algae) | 1.9 µg/L | 4 µg/L |
| Maximum Depth | 107 ft | 45 ft |
| Surface Area | 536 acres | 1,267 acres |
| Public Access | No | Yes |
| Fish Species | 13 | 14 |
| Trophic State | oligotrophic | 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 Deep Lake: 19.4 ft, Birch Lake: 14 ft) and what you want from the lake. Big Deep Lake has fewer fish species than Birch Lake.
Source: EPA National Aquatic Resource Surveys, 2026.