Big Lake vs Colby Lake
Water quality, depth, fish species, and recreation comparison.
Big Lake and Colby Lake both received the same overall water quality grade of A (Excellent). Both are in St. Louis County, Minnesota.
Big Lake and Colby 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. These two are within a letter of each other on the rubric — Big Lake (A) versus Colby Lake (A). The deciding factors for a recreational visitor are likely physical (depth, access, fish species) rather than water-quality differences.
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 Lake
Moderate clarity, visible to about 8.2 ft.
Colby Lake
Very murky, less than 3 ft of visibility.
Side-by-Side Metrics
| Metric | Big Lake | Colby Lake |
|---|---|---|
| Overall Grade | A (Excellent) | A (Excellent) |
| Water Clarity | 8.2 ft | 3 ft |
| Phosphorus | 14 µg/L | 22 µg/L |
| Chlorophyll-a (Algae) | 4.9 µg/L | 3.2 µg/L |
| Maximum Depth | 22 ft | 30 ft |
| Surface Area | 1,904 acres | 518 acres |
| Public Access | Yes | Yes |
| Fish Species | 8 | 15 |
| Trophic State | mesotrophic | eutrophic |
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 Lake: 8.2 ft, Colby Lake: 3 ft) and what you want from the lake. Big Lake has fewer fish species than Colby Lake.
Source: EPA National Aquatic Resource Surveys, 2026.