Rainy Lake

Rainy Lake sits at a C on the grading scale — not impaired, not pristine, with summer measurements that vary year to year. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

Mesotrophic conditions dominate at Rainy Lake: enough nutrients for a healthy fishery, not so much that algal blooms become a chronic problem. At 161 ft of maximum depth, Rainy Lake stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. At 210,200 acres, Rainy Lake is one of the larger lakes in St. Louis County, with 2176.3 miles of shoreline supporting multiple distinct use patterns. Among the 187 graded lakes in St. Louis County, Rainy Lake sits at rank 90, above the county median.

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 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. 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.