Is Blackduck Lake Safe for Swimming?
Blackduck Lake in St. Louis County, Minnesota has a water quality grade of D (Poor). Swimming not recommended, poor water quality with high algae risk. Water clarity: 6.8 ft visibility. Phosphorus: 43 µg/L. Chlorophyll-a (algae): 23.3 µg/L. Always check local health department advisories before swimming.
Key Metrics
| Metric | Value |
|---|---|
| Overall Grade | D (Poor) |
| Water Clarity (Secchi Depth) | 6.8 ft |
| Phosphorus | 43 μg/L |
| Chlorophyll-a (Algae) | 23.3 μg/L |
| Maximum Depth | 30 ft |
| Location | St. Louis County, Minnesota |
How does Blackduck Lake compare?
With an overall water quality grade of D, Blackduck Lake falls below the Minnesota state average of Grade C. It ranks #66 of 68 lakes in St. Louis County by water quality score.
Water clarity (Secchi depth) sits at 6.8 feet. That puts the lake in good clarity range, with limited algae interference. Algae levels (chlorophyll-a) measure 23.3 µg/L — elevated; risk of harmful algal bloom advisories increases at this concentration.