Big Lake vs Birch Lake
Water quality, depth, fish species, and recreation comparison.
Big Lake has a higher water quality grade (A, Excellent) than Birch Lake (C, Fair). Both are in St. Louis County, Minnesota.
Both Big 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. Big Lake (A) is materially cleaner than Birch Lake (C). A gap that wide is unlikely to close in a single year of remediation work; it reflects multi-decade differences in the lakes themselves.
For a recreational visitor, the wider grade gap is decisive — Big Lake is the better water-quality choice. For a researcher, the gap is the interesting part: what is different about the two watersheds, and which of those differences is mutable?
Big Lake
Moderate clarity, visible to about 8.2 ft.
Birch Lake
Murky, only visible to about 3.9 ft.
Side-by-Side Metrics
| Metric | Big Lake | Birch Lake |
|---|---|---|
| Overall Grade | A (Excellent) | C (Fair) |
| Water Clarity | 8.2 ft | 3.9 ft |
| Phosphorus | 14 µg/L | 21.5 µg/L |
| Chlorophyll-a (Algae) | 4.9 µg/L | 7.5 µg/L |
| Maximum Depth | 22 ft | 25 ft |
| Surface Area | 1,904 acres | 7,074 acres |
| Public Access | Yes | Yes |
| Fish Species | 8 | 10 |
| Trophic State | mesotrophic | eutrophic |
Bold value = better for that metric (lower phosphorus / chlorophyll = cleaner; higher Secchi / depth / species count = better).
Verdict
Big Lake wins on overall water quality with a Grade A versus Birch Lake's Grade C. Water clarity: 8.2 ft vs 3.9 ft. For more fish-species variety, Birch Lake edges ahead with 10 documented species.
Source: EPA National Aquatic Resource Surveys, 2026.