Big Lake vs Turtle River Lake
Water quality, depth, fish species, and recreation comparison.
Big Lake has a higher water quality grade (A, Excellent) than Turtle River Lake (C, Fair). Both are in Beltrami County, Minnesota.
Big Lake and Turtle River 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. Big Lake (A) is materially cleaner than Turtle River 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?
Big Lake
Moderate clarity, visible to about 9.7 ft.
Turtle River Lake
Moderate clarity, visible to about 8.5 ft.
Side-by-Side Metrics
| Metric | Big Lake | Turtle River Lake |
|---|---|---|
| Overall Grade | A (Excellent) | C (Fair) |
| Water Clarity | 9.7 ft | 8.5 ft |
| Phosphorus | 15 µg/L | 18.5 µg/L |
| Chlorophyll-a (Algae) | 4.8 µg/L | 7.5 µg/L |
| Maximum Depth | 35 ft | 63 ft |
| Surface Area | 3,598 acres | 1,740 acres |
| Public Access | Yes | Yes |
| Fish Species | 17 | 20 |
| Trophic State | mesotrophic | 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 Turtle River Lake's Grade C. Water clarity: 9.7 ft vs 8.5 ft. For more fish-species variety, Turtle River Lake edges ahead with 20 documented species.
Source: EPA National Aquatic Resource Surveys, 2026.