Thompson Lake

Thompson Lake earns an F: phosphorus readings still being added and clarity at 3.0 ft signal heavy nutrient loading from the surrounding watershed. Sub-grades cluster within a single letter of each other, which usually means the lake is in stable trophic balance rather than fighting one specific stressor.

Eutrophic conditions are the baseline here: clarity drops noticeably in late summer, and dissolved oxygen near the bottom can become a concern. Thompson Lake is a shallow lake at 9 ft maximum depth, which means it warms quickly, mixes constantly, and amplifies nutrient inputs. At 207 acres, Thompson Lake fits the Minnesota median for monitored lakes, with 3.9 miles of shoreline. Thompson Lake ranks 180 of 187 in St. Louis County — at the lower end of the locally monitored distribution.

Thompson Lake has no invasive species recorded in Minnesota state databases as of 2023, though prevention practices still apply at all access points. The fishery is bass-led, with 8 documented species across the lake's records. No formal public access is documented at Thompson Lake — most use is by shoreline residents and their guests. The lake has a partial ice record — 11 observed ice-outs, centered near Apr 23. 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.