Rainy Lake

Rainy Lake pulls a D on the LakeGrade rubric — phosphorus loading and limited clarity hold it below the Minnesota average. Sub-grades cluster within a single letter of each other, which usually means the lake is in stable trophic balance rather than fighting one specific stressor.

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 161 ft maximum depth is in the upper tier for Minnesota — deep enough for cold-water fish to find refuge in summer. Rainy Lake covers 210,200 acres alongside 2176.3 miles of shoreline, large enough that conditions can vary meaningfully between bays. Rainy Lake sits at rank 5 of 7 in Koochiching County, in the lower half of the local distribution.

Zebra mussels have been documented at Rainy Lake, which alters the filter-feeding balance and can paradoxically increase water clarity while disrupting the food web. Walleye are documented at Rainy 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 Rainy Lake more than two dozen times, putting the median around May 4 — 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.