Armstrong Lake

Armstrong Lake earns an A — water clarity, phosphorus, and chlorophyll-a all rate among the best monitored waters in St. Louis County. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

A TSI value of 37 puts Armstrong Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. Armstrong Lake reaches 34 ft at its deepest point — typical for Minnesota mid-sized lakes, with seasonal stratification but limited cold-water refuge. At 382 acres, Armstrong Lake fits the Minnesota median for monitored lakes, with 4.5 miles of shoreline. Armstrong Lake ranks 13 of 187 in St. Louis County, putting it in the upper tier of locally monitored lakes.

No invasive species are currently listed at Armstrong Lake — the lake remains off the Minnesota infested-waters roster. The fishery includes walleye alongside the lake's other 10 documented species — a notable draw for Minnesota anglers. A documented public access point at Armstrong Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.