Deep Portage Lake

Deep Portage 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 38 puts Deep Portage Lake in the oligotrophic range, where biological productivity stays low and the water column remains clear. At 105 ft of maximum depth, Deep Portage Lake stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. At 129 acres, Deep Portage Lake fits the Minnesota median for monitored lakes, with 1.8 miles of shoreline. Deep Portage Lake ranks 1 of 133 in Cass County, putting it in the upper tier of locally monitored lakes.

Deep Portage Lake has no invasive species recorded in Minnesota state databases as of 2024, though prevention practices still apply at all access points. The fishery includes walleye alongside the lake's other 9 documented species — a notable draw for Minnesota anglers. No formal public access is documented at Deep Portage Lake — most use is by shoreline residents and their guests. 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.