Rainy Lake

Rainy Lake pulls a D on the LakeGrade rubric — phosphorus loading and limited clarity hold it below the Minnesota average.

Eutrophic conditions are the baseline here: clarity drops noticeably in late summer, and dissolved oxygen near the bottom can become a concern. 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. At 210,200 acres, Rainy Lake is one of the larger lakes in Koochiching County, with 2176.3 miles of shoreline supporting multiple distinct use patterns. Within Koochiching County's 7 graded lakes, Rainy Lake ranks 5 — below the local median, though not at the bottom.

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. The fishery includes walleye among the lake's 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. The lake has a long ice-out record — 106 observations on file, with a median ice-out around May 4. 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.