Seven Island Lake

Seven Island Lake sits at the top of the Wisconsin DNR grading rubric with an A, a mark reached by the cleanest lakes in Wisconsin. The two scored sub-grades — clarity and phosphorus — track close together, so neither one is dragging the average down.

A TSI value of 38 puts Seven Island Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. Seven Island Lake reaches 31 ft at its deepest point — typical for Wisconsin mid-sized lakes, with seasonal stratification but limited cold-water refuge. The lake's 132 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 18 graded lakes in Lincoln County, Seven Island Lake sits at rank 7, above the county median.

Eurasian watermilfoil has been documented at Seven Island Lake, requiring shoreline management to keep dense mats from crowding native vegetation. Walleye are documented at Seven Island Lake, one of 5 fish species on record for the lake. 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.