Rainy Lake

Rainy Lake earns a D — measurements through 2023 show persistent nutrient pressure that limits clarity through the summer.

At a TSI of 50, Rainy Lake reads as eutrophic — nutrient-rich enough that summer algal growth and reduced clarity are expected, not unusual. 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. Within Koochiching County's 7 graded lakes, Rainy Lake ranks 4 — below the local median, though not at the bottom.

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. 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. 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.