Rainy Lake

The LakeGrade rubric puts Rainy Lake at a C: clarity at 9.5 ft, phosphorus readings still being added, and a TSI of 45 signal an intermediate trophic state. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

The lake sits in the mesotrophic zone — the band where most well-managed Minnesota lakes fall. Rainy Lake is unusually deep for Minnesota at 161 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. With 210,200 acres of surface and 2176.3 miles of shoreline, Rainy Lake is a large water by Minnesota standards — recreational pressure is spread across a long shoreline. Rainy Lake ranks 85 of 187 in St. Louis County — solidly in the upper half of the local distribution.

Zebra mussel presence at Rainy Lake means the lake's clarity numbers carry an asterisk — filtered water is not the same as nutrient-poor water. The fishery includes walleye alongside the lake's other 17 documented species — a notable draw for Minnesota anglers. A documented public access point at Rainy Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. 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. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.