Cass Lake

Cass Lake earns an A — water clarity, phosphorus, and chlorophyll-a all rate among the best monitored waters in Beltrami County. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

The lake's low TSI puts it in oligotrophic territory — the cleanest of the four trophic classes, but also the most vulnerable to nutrient-driven shifts. The lake's 120 ft maximum depth is in the upper tier for Minnesota — deep enough for cold-water fish to find refuge in summer. With 15,958 acres of surface and 45.4 miles of shoreline, Cass Lake is a large water by Minnesota standards — recreational pressure is spread across a long shoreline. Cass Lake ranks 19 of 95 in Beltrami County, putting it in the upper tier of locally monitored lakes.

Zebra mussels have been documented at Cass Lake, which alters the filter-feeding balance and can paradoxically increase water clarity while disrupting the food web. Cass Lake's fishery is anchored by muskellunge, with 21 documented species in total — a destination water for muskie anglers. A documented public access point at Cass Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. The lake has a partial ice record — 10 observed ice-outs, centered near Apr 24. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.