Big Portage (W Bay Lake vs Birch Lake
Water quality, depth, fish species, and recreation comparison.
Big Portage (W Bay Lake and Birch Lake both received the same overall water quality grade of A (Excellent). Both are in Cass County, Minnesota.
Both Big Portage (W Bay 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. The grades are close: Big Portage (W Bay Lake (A) and Birch Lake (A) are within one letter of each other on the LakeGrade rubric. The per-parameter sub-grades below will show where the small differences actually live.
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 Portage (W Bay Lake
Moderate clarity, visible to about 8.5 ft.
Birch Lake
Good clarity, visible to about 14 ft.
Side-by-Side Metrics
| Metric | Big Portage (W Bay Lake | Birch Lake |
|---|---|---|
| Overall Grade | A (Excellent) | A (Excellent) |
| Water Clarity | 8.5 ft | 14 ft |
| Phosphorus | 18.5 µg/L | 12 µg/L |
| Chlorophyll-a (Algae) | 5.6 µg/L | 4 µg/L |
| Maximum Depth | 23 ft | 45 ft |
| Surface Area | 902 acres | 1,267 acres |
| Public Access | Yes | Yes |
| Fish Species | 13 | 14 |
| Trophic State | mesotrophic | 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 Portage (W Bay Lake: 8.5 ft, Birch Lake: 14 ft) and what you want from the lake. Big Portage (W Bay Lake has fewer fish species than Birch Lake.
Source: EPA National Aquatic Resource Surveys, 2026.