Madison Lake

On the scoring rubric Madison Lake grades a D: clarity at 3.6 ft and 75 µg/L of phosphorus keep it in the lower bracket for Blue Earth County. Sub-grades cluster within a single letter of each other, which usually means the lake is in stable trophic balance rather than fighting one specific stressor.

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's 59 ft maximum depth is in the upper tier for Minnesota — deep enough for cold-water fish to find refuge in summer. With 1,447 acres of surface and 12.5 miles of shoreline, Madison Lake is a large water by Minnesota standards — recreational pressure is spread across a long shoreline. Within Blue Earth County's 9 graded waters, Madison Lake sits at rank 2, near the top of the local distribution.

Madison Lake carries an invasive watermilfoil record — boat-launch decontamination and shoreline care matter more here than at uninfested lakes. Walleye are documented at Madison Lake, one of 20 fish species on record for the lake. Public access is available — the lake is on the Minnesota PCA public-access list. The lake has a long ice-out record — 109 observations on file, with a median ice-out around Apr 6. 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.