Birch Lake vs Portage Lake
Water quality, depth, fish species, and recreation comparison.
Birch Lake reads lower on nutrients and algae than Portage Lake. Both are in Cass County, Minnesota.
Birch Lake and Portage Lake 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. The readings are meaningfully apart: Birch Lake carries clearly lower phosphorus and chlorophyll-a readings than Portage Lake. A spread that wide reflects real underlying differences, in watershed inputs, depth profiles, or monitoring rigor.
For a recreational visitor, the wider gap in the readings is decisive: Birch 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?
Birch Lake
Good clarity, visible to about 14 ft.
Portage Lake
Moderate clarity, visible to about 7.5 ft.
Side-by-Side Metrics
| Metric | Birch Lake | Portage Lake |
|---|---|---|
| Water Clarity | 14 ft Better | 7.5 ft |
| Phosphorus | 12 µg/L Better | 22 µg/L |
| Chlorophyll-a (Algae) | 4 µg/L Better | 7.1 µg/L |
| Maximum Depth | 45 ft | 55 ft Better |
| Surface Area | 1,267 acres | 1,539 acres |
| Public Access | Yes | Yes |
| Fish Species | 14 | 15 Better |
| Trophic State | mesotrophic | mesotrophic |
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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Compare Birch Lake or Portage Lake against a different lake.
Verdict
Birch Lake reads lower on nutrients and algae than Portage Lake. Water clarity: 14 ft vs 7.5 ft. For more fish-species variety, Portage Lake edges ahead with 15 documented species.
Source: EPA National Aquatic Resource Surveys, 2026.