St. Mary'S Lake

St. Mary'S 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.

Trophically, St. Mary'S Lake reads as oligotrophic — nutrient-poor, clear, and ecologically more sensitive to disturbance than richer lakes. St. Mary'S Lake reaches 44 ft at its deepest point — typical for Minnesota mid-sized lakes, with seasonal stratification but limited cold-water refuge. At 234 acres, St. Mary'S Lake fits the Minnesota median for monitored lakes, with 4.1 miles of shoreline. Within St. Louis County's 187 graded waters, St. Mary'S Lake sits at rank 21, near the top of the local distribution.

No invasive species are currently listed at St. Mary'S Lake — the lake remains off the Minnesota infested-waters roster. Walleye are documented at St. Mary'S Lake, one of 14 fish species on record for the lake. The lake lacks a documented public access point, so visitor use is limited. The lake has a partial ice record — 9 observed ice-outs, centered near Apr 24. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.