Iron Lake

Iron Lake earns a D — measurements through 2025 show persistent nutrient pressure that limits clarity through the summer. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

Eutrophic conditions are the baseline here: clarity drops noticeably in late summer, and dissolved oxygen near the bottom can become a concern. Iron Lake is unusually deep for Minnesota at 64 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. At 1,962 acres, Iron Lake is one of the larger lakes in St. Louis County, with 53.5 miles of shoreline supporting multiple distinct use patterns. Within the 215 graded lakes of St. Louis County, Iron Lake sits at rank 199, near the bottom of the county list.

Iron Lake has at least one documented invasive species (spiny waterflea), so boaters and anglers should observe clean-drain-dry steps when leaving the lake. The fishery includes walleye alongside the lake's other 9 documented species — a notable draw for Minnesota anglers. The lake lacks a documented public access point, so visitor use is limited. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.