Rainy Lake

On the scoring rubric Rainy Lake grades a D: clarity at 5.9 ft and phosphorus readings still being added keep it in the lower bracket for St. Louis County. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

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. At 161 ft of maximum depth, Rainy Lake stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. 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 sits at rank 159 of 215 in St. Louis County, in the lower half of the local distribution.

Rainy Lake is on the Minnesota infested-waters list for zebra mussels — boaters should follow clean-drain-dry protocols when moving gear to or from the lake. The fishery includes walleye alongside the lake's other 17 documented species — a notable draw for Minnesota anglers. Public access is available — the lake is on the Minnesota PCA public-access list. The lake has a long ice-out record — 106 observations on file, with a median ice-out around May 4. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.