Big Lake vs Johnson Lake
Water quality, depth, fish species, and recreation comparison.
Big Lake has a higher water quality grade (A, Excellent) than Johnson Lake (C, Fair). Both are in St. Louis County, Minnesota.
Big Lake and Johnson 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 grades are meaningfully apart: Big Lake grades a A while Johnson Lake grades a C. That two-letter spread reflects real underlying differences — different watershed inputs, different depth profiles, or different monitoring rigor.
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 8.2 ft.
Johnson Lake
Very murky, less than 3 ft of visibility.
Side-by-Side Metrics
| Metric | Big Lake | Johnson Lake |
|---|---|---|
| Overall Grade | A (Excellent) | C (Fair) |
| Water Clarity | 8.2 ft | 3 ft |
| Phosphorus | 14 µg/L | 33 µg/L |
| Chlorophyll-a (Algae) | 4.9 µg/L | 9.8 µg/L |
| Maximum Depth | 22 ft | 18 ft |
| Surface Area | 1,904 acres | 456 acres |
| Public Access | Yes | Yes |
| Fish Species | 8 | 11 |
| Trophic State | mesotrophic | eutrophic |
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 Johnson Lake's Grade C. Water clarity: 8.2 ft vs 3 ft. For more fish-species variety, Johnson Lake edges ahead with 11 documented species.
Source: EPA National Aquatic Resource Surveys, 2026.