Big Lake vs Birch Lake
Water quality, depth, fish species, and recreation comparison.
Big Lake reads lower on nutrients and algae than Birch Lake. 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 differences in the readings here are about the lakes themselves, not the agencies sampling them. Big Lake reads materially cleaner than Birch Lake on nutrients and algae. 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 gap in the readings is decisive: Big Lake has the lower nutrient and algae numbers. 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 |
|---|---|---|
| Water Clarity | 8.2 ft Better | 3.9 ft |
| Phosphorus | 14 µg/L Better | 21.5 µg/L |
| Chlorophyll-a (Algae) | 4.9 µg/L Better | 7.5 µg/L |
| Maximum Depth | 22 ft | 25 ft Better |
| Surface Area | 1,904 acres | 7,074 acres |
| Public Access | Yes | Yes |
| Fish Species | 8 | 10 Better |
| Trophic State | mesotrophic | eutrophic |
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.
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Verdict
Big Lake reads lower on nutrients and algae than Birch Lake. Water clarity: 8.2 ft vs 3.9 ft. For more fish-species variety, Birch Lake edges ahead with 10 documented species.
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Source: EPA National Aquatic Resource Surveys, 2026.