How Clean Is Johnson Lake?
Johnson Lake has fair water quality — typical of lakes with moderate nutrient enrichment. It received a water quality grade of C (Fair) based on EPA monitoring data. Water clarity (Secchi depth): 3 ft. Phosphorus: 33 µg/L. Chlorophyll-a (algae): 9.8 µg/L. Trophic State Index: 56.
Cleanliness Snapshot
| Metric | Johnson Lake | Minnesota avg |
|---|---|---|
| Overall Grade | C | C |
| Water Clarity (Secchi) | 3 ft | — |
| Phosphorus | 33 µg/L | <30 = clean |
| Chlorophyll-a (Algae) | 9.8 µg/L | <10 = clean |
| Trophic State Index | 56 | <50 = clean |
How does Johnson Lake compare?
Johnson Lake's grade of C matches or beats the Minnesota state average of C. It ranks #50 of 68 lakes in St. Louis County by water quality score. Multi-year monitoring data shows water quality is declining based on 3 years of records.