St. Johns Lake

On the LakeGrade rubric, St. Johns Lake pulls an A: clarity at 10.2 ft and 15 µg/L of phosphorus put it in the top bracket for Wisconsin. The two scored sub-grades — clarity and phosphorus — track close together, so neither one is dragging the average down.

A TSI near 43 places St. Johns Lake in the mesotrophic band — moderate productivity, with seasonal swings between clearer spring water and richer late-summer conditions. St. Johns Lake reaches 21 ft at its deepest point — typical for Wisconsin mid-sized lakes, with seasonal stratification but limited cold-water refuge. The lake's 107 acres and partial shoreline records put it in the mid-range bucket — large enough for varied use, small enough that watershed inputs reach the whole basin. Among the 34 graded lakes in Forest County, St. Johns Lake sits at rank 11, above the county median.

No invasive species are currently listed at St. Johns Lake — the lake remains off the Wisconsin infested-waters roster. Walleye are documented at St. Johns Lake, one of 3 fish species on record for the lake. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.