Lac la Croix Lake

Lac la Croix Lake earns an F: phosphorus readings still being added and clarity at 2.5 ft signal heavy nutrient loading from the surrounding watershed. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

A TSI in the eutrophic range signals a lake doing what nutrient-loaded waters do — supporting an active algal community at the cost of clear water. The lake bottoms out at 30 ft — a moderate depth that supports a warm-water fishery without the year-round cold refuge a deeper basin provides. At 1,045 acres, Lac la Croix Lake is one of the larger lakes in St. Louis County, with 13.0 miles of shoreline supporting multiple distinct use patterns. Within the 215 graded lakes of St. Louis County, Lac la Croix Lake sits at rank 207, near the bottom of the county list.

Lac la Croix Lake has no invasive species recorded in Minnesota state databases as of 2025, though prevention practices still apply at all access points. Walleye are documented at Lac la Croix Lake, one of 10 fish species on record for the lake. 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.