How Clean Is Colby Lake?
Colby Lake is among the cleanest lakes in Minnesota. It received a water quality grade of A (Excellent) based on EPA monitoring data. Water clarity (Secchi depth): 3 ft. Phosphorus: 22 µg/L. Chlorophyll-a (algae): 3.2 µg/L. Trophic State Index: 51.
Cleanliness Snapshot
| Metric | Colby Lake | Minnesota avg |
|---|---|---|
| Overall Grade | A | C |
| Water Clarity (Secchi) | 3 ft | — |
| Phosphorus | 22 µg/L | <30 = clean |
| Chlorophyll-a (Algae) | 3.2 µg/L | <10 = clean |
| Trophic State Index | 51 | <50 = clean |
How does Colby Lake compare?
Colby Lake's grade of A matches or beats the Minnesota state average of C. It ranks #3 of 68 lakes in St. Louis County by water quality score. Multi-year monitoring data shows water quality is declining based on 6 years of records.