How Clean Is Lake St. Louis?
Lake St. Louis has poor water quality, with elevated phosphorus and algae. It received a water quality grade of D (Poor) based on EPA monitoring data. Water clarity (Secchi depth): 2.7 ft. Phosphorus: 50 µg/L. Chlorophyll-a (algae): 74.3 µg/L. Trophic State Index: 65.
Cleanliness Snapshot
| Metric | Lake St. Louis | Missouri avg |
|---|---|---|
| Overall Grade | D | C |
| Water Clarity (Secchi) | 2.7 ft | — |
| Phosphorus | 50 µg/L | <30 = clean |
| Chlorophyll-a (Algae) | 74.3 µg/L | <10 = clean |
| Trophic State Index | 65 | <50 = clean |
How does Lake St. Louis compare?
Lake St. Louis's grade of D falls below the Missouri state average of C. It ranks #7 of 11 lakes in St. Charles County by water quality score. Multi-year monitoring data shows water quality is declining based on 5 years of records.