Marion Lake

Marion Lake sits at the top of the Minnesota PCA grading rubric with an A, a mark reached by the cleanest lakes in Minnesota. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

The lake sits in the mesotrophic zone — the band where most well-managed Minnesota lakes fall. At 62 ft of maximum depth, Marion Lake stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. At 1,624 acres, Marion Lake is one of the larger lakes in Otter Tail County, with 9.1 miles of shoreline supporting multiple distinct use patterns. Marion Lake ranks 29 of 97 in Otter Tail County — solidly in the upper half of the local distribution.

Zebra mussels have been documented at Marion Lake, which alters the filter-feeding balance and can paradoxically increase water clarity while disrupting the food web. Walleye are documented at Marion Lake, one of 17 fish species on record for the lake. Public access is available — the lake is on the Minnesota PCA public-access list. Ice-out has been logged at Marion Lake more than two dozen times, putting the median around Apr 16 — 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.