Ash Lake vs Big Lake
Water quality, depth, fish species, and recreation comparison.
Big Lake has a higher water quality grade (A, Excellent) than Ash Lake (C, Fair). Both are in St. Louis County, Minnesota.
Both Ash Lake and Big 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 Ash 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?
Ash Lake
Murky, only visible to about 5.5 ft.
Big Lake
Moderate clarity, visible to about 8.2 ft.
Side-by-Side Metrics
| Metric | Ash Lake | Big Lake |
|---|---|---|
| Overall Grade | C (Fair) | A (Excellent) |
| Water Clarity | 5.5 ft | 8.2 ft |
| Phosphorus | 39 µg/L | 14 µg/L |
| Chlorophyll-a (Algae) | 11.1 µg/L | 4.9 µg/L |
| Maximum Depth | 25 ft | 22 ft |
| Surface Area | 690 acres | 1,904 acres |
| Public Access | Yes | Yes |
| Fish Species | 9 | 8 |
| Trophic State | eutrophic | mesotrophic |
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 Ash Lake's Grade C. Water clarity: 8.2 ft vs 5.5 ft. For more fish-species variety, Ash Lake edges ahead with 9 documented species.
Source: EPA National Aquatic Resource Surveys, 2026.