Mason Lake

Mason Lake sits at a C on the grading scale — not impaired, not pristine, with summer measurements that vary year to year. Secchi readings are the weakest of the three parameters, suggesting suspended sediment or algal biomass dominates the optical signal.

A TSI in the eutrophic range signals a lake doing what nutrient-loaded waters do — supporting an active algal community at the cost of clear water. The lake's 108 ft maximum depth is in the upper tier for Minnesota — deep enough for cold-water fish to find refuge in summer. With 5,615 acres of surface and 17.1 miles of shoreline, Mason Lake is a large water by Minnesota standards — recreational pressure is spread across a long shoreline. Within the 97 graded lakes of Otter Tail County, Mason Lake sits at rank 87, near the bottom of the county list.

Zebra mussel presence at Mason Lake means the lake's clarity numbers carry an asterisk — filtered water is not the same as nutrient-poor water. Muskie are on the species list at Mason Lake, alongside the lake's 17 other documented fish. A documented public access point at Mason Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. Ice-out has been logged at Mason Lake more than two dozen times, putting the median around Apr 15 — a useful baseline for tracking climate trends. 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.