Is Big Deep Lake Safe for Swimming?
Big Deep Lake in Cass County, Minnesota has a water quality grade of A (Excellent). Excellent for swimming, crystal clear water with minimal algae. Water clarity: 19.4 ft visibility. Phosphorus: 7 µg/L. Chlorophyll-a (algae): 1.9 µg/L. Always check local health department advisories before swimming.
Key Metrics
| Metric | Value |
|---|---|
| Overall Grade | A (Excellent) |
| Water Clarity (Secchi Depth) | 19.4 ft |
| Phosphorus | 7 μg/L |
| Chlorophyll-a (Algae) | 1.9 μg/L |
| Maximum Depth | 107 ft |
| Location | Cass County, Minnesota |
How does Big Deep Lake compare?
With an overall water quality grade of A, Big Deep Lake matches or beats the Minnesota state average of Grade C. It ranks #85 of 104 lakes in Cass County by water quality score.
Water clarity (Secchi depth) sits at 19.4 feet. That counts as exceptional clarity — sunlight penetrates deep, supporting submerged plants and limiting algae. Algae levels (chlorophyll-a) measure 1.9 µg/L — low and well within safe swimming guidelines.