Big Lake vs Upper Estuary Lake
Water quality, depth, fish species, and recreation comparison.
Big Lake has a higher water quality grade (A, Excellent) than Upper Estuary Lake (C, Fair). Both are in St. Louis County, Minnesota.
Big Lake and Upper Estuary 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 Upper Estuary 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.
Upper Estuary Lake
Very murky, less than 1.9 ft of visibility.
Side-by-Side Metrics
| Metric | Big Lake | Upper Estuary Lake |
|---|---|---|
| Overall Grade | A (Excellent) | C (Fair) |
| Water Clarity | 8.2 ft | 1.9 ft |
| Phosphorus | 14 µg/L | 49.5 µg/L |
| Chlorophyll-a (Algae) | 4.9 µg/L | 1.7 µg/L |
| Maximum Depth | 22 ft | 55 ft |
| Surface Area | 1,904 acres | 10,255 acres |
| Public Access | Yes | Yes |
| Fish Species | 8 | 33 |
| 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 Upper Estuary Lake's Grade C. Water clarity: 8.2 ft vs 1.9 ft. For more fish-species variety, Upper Estuary Lake edges ahead with 33 documented species.
Source: EPA National Aquatic Resource Surveys, 2026.