Is Mark Twain Lake Safe for Swimming?
Mark Twain Lake in Ralls County, Wisconsin has a water quality grade of D (Poor). Swimming not recommended, poor water quality with high algae risk. Water clarity: 2.5 ft visibility. Phosphorus: 60.8 µg/L. Chlorophyll-a (algae): 18.3 µg/L. Always check local health department advisories before swimming.
Key Metrics
| Metric | Value |
|---|---|
| Overall Grade | D (Poor) |
| Water Clarity (Secchi Depth) | 2.5 ft |
| Phosphorus | 60.8 μg/L |
| Chlorophyll-a (Algae) | 18.3 μg/L |
| Location | Ralls County, Wisconsin |
How does Mark Twain Lake compare?
With an overall water quality grade of D, Mark Twain Lake falls below the Wisconsin state average of Grade C. It ranks #3 of 4 lakes in Ralls County by water quality score.
Water clarity (Secchi depth) sits at 2.5 feet. That signals heavy algae or sediment, often tied to high phosphorus from runoff. Algae levels (chlorophyll-a) measure 18.3 µg/L — moderate; acceptable for swimming on most days, but worth checking advisories.