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Bear Island Lake reads lower on nutrients and algae than Birch Lake. Both are in St. Louis County, Minnesota.

Reviewed by LakeQuality Editorial Team · Updated

Bear Island Lake and Birch 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: Bear Island Lake carries clearly lower phosphorus and chlorophyll-a readings than Birch 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: Bear Island 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?

Bear Island Lake

St. Louis County, Minnesota

Moderate clarity, visible to about 7 ft.

Birch Lake

St. Louis County, Minnesota

Murky, only visible to about 3.9 ft.

Side-by-Side Metrics

MetricBear Island LakeBirch Lake
Water Clarity7 ft Better3.9 ft
Phosphorus15 µg/L Better21.5 µg/L
Chlorophyll-a (Algae)6.4 µg/L Better7.5 µg/L
Maximum Depth62 ft Better25 ft
Surface Area2,362 acres7,074 acres
Public AccessYesYes
Fish Species13 Better10
Trophic Statemesotrophiceutrophic

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.

Verdict

Bear Island Lake reads lower on nutrients and algae than Birch Lake. Water clarity: 7 ft vs 3.9 ft. For fishing diversity, Bear Island Lake also leads with 13 species.

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Where to stay near Bear Island Lake and Birch Lake

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Source: EPA National Aquatic Resource Surveys, 2026.