Big Lake

Big Lake carries a solid B grade — strong on most parameters, with measurements that hold up well across the summer season. The lake's weakest score is on Secchi depth — the water looks more turbid than its phosphorus number alone would predict.

Mesotrophic conditions dominate at Big Lake: enough nutrients for a healthy fishery, not so much that algal blooms become a chronic problem. Big Lake reaches 22 ft at its deepest point — typical for Minnesota mid-sized lakes, with seasonal stratification but limited cold-water refuge. With 1,904 acres of surface and 25.9 miles of shoreline, Big Lake is a large water by Minnesota standards — recreational pressure is spread across a long shoreline. Among the 215 graded lakes in St. Louis County, Big Lake ranks 53 — in the top quartile locally.

Big Lake has no invasive species recorded in Minnesota state databases as of 2025, though prevention practices still apply at all access points. The fishery includes walleye alongside the lake's other 8 documented species — a notable draw for Minnesota anglers. Public access is available — the lake is on the Minnesota PCA public-access list. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.