Oak Lake

Oak Lake earns an F: 144 µg/L of phosphorus and clarity at 3.0 ft signal heavy nutrient loading from the surrounding watershed. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

Eutrophic conditions are the baseline here: clarity drops noticeably in late summer, and dissolved oxygen near the bottom can become a concern. The lake's maximum depth is not yet documented in state morphometric records — context for its physical structure remains limited. The lake's surface area is not consistently recorded across state datasets — physical context remains partial. Within the 20 graded lakes of Polk County, Oak Lake sits at rank 19, near the bottom of the county list.

Oak Lake has no invasive species recorded in Minnesota state databases as of 2024, though prevention practices still apply at all access points. The state fisheries records do not list documented species for Oak Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. No formal public access is documented at Oak Lake — most use is by shoreline residents and their guests. Ice-out has been recorded 10 times at Oak Lake, with a median around Apr 12. 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.