Gunflint Lake

On the LakeGrade rubric, Gunflint Lake pulls an A: clarity at 20.0 ft and phosphorus readings still being added put it in the top bracket for Minnesota.

The lake's low TSI puts it in oligotrophic territory — the cleanest of the four trophic classes, but also the most vulnerable to nutrient-driven shifts. Gunflint Lake is unusually deep for Minnesota at 200 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. At 4,009 acres, Gunflint Lake is one of the larger lakes in Cook County, with 39.2 miles of shoreline supporting multiple distinct use patterns. Within Cook County's 128 graded waters, Gunflint Lake sits at rank 14, near the top of the local distribution.

An invasive species record — spiny waterflea — has been logged at Gunflint Lake; Minnesota PCA maintains the official infested-waters list. The fishery includes walleye among the lake's 12 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 — 81 observations on file, with a median ice-out around May 6. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.