Duncan Lake

Duncan 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.

Trophically, Duncan Lake reads as oligotrophic — nutrient-poor, clear, and ecologically more sensitive to disturbance than richer lakes. Duncan Lake is unusually deep for Minnesota at 130 ft, which buffers the lake against summer warming and helps the deep water stay oxygenated. At 477 acres, Duncan Lake fits the Minnesota median for monitored lakes, with 7.6 miles of shoreline. Within Cook County's 128 graded waters, Duncan Lake sits at rank 10, near the top of the local distribution.

Duncan Lake has no invasive species recorded in Minnesota state databases as of 2024, though prevention practices still apply at all access points. The fishery is bass-led, with 5 documented species across the lake's records. No formal public access is documented at Duncan 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.