Three Island Lake

Three Island Lake sits at the top of the Minnesota PCA grading rubric with an A, a mark reached by the cleanest lakes in Minnesota. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

A TSI value of 29 puts Three Island Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. Three Island Lake is unusually deep for Minnesota at 66 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. Three Island Lake covers 250 acres alongside 3.8 miles of shoreline — a mid-sized water that supports a working fishery without being so large that conditions diverge between basins. Three Island Lake ranks 23 of 141 in Itasca County, putting it in the upper tier of locally monitored lakes.

No invasive species are currently listed at Three Island Lake — the lake remains off the Minnesota infested-waters roster. The fishery includes walleye alongside the lake's other 7 documented species — a notable draw for Minnesota anglers. The lake lacks a documented public access point, so visitor use is limited. 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.