Thompson Lake

On the LakeGrade rubric Thompson Lake fails the cutoffs — a TSI of 62 and persistent algal pressure put it in the bottom tier. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

Eutrophic conditions are the baseline here: clarity drops noticeably in late summer, and dissolved oxygen near the bottom can become a concern. A maximum depth of just 8 ft means sediment-bound phosphorus releases back into the water column whenever wind stirs the bottom — a classic shallow-lake dynamic. At 8 acres, Thompson Lake sits below the Minnesota median: a small water where shoreline activity has an outsized effect on water quality. Thompson Lake sits at rank 26 of 36 in Dakota County, in the lower half of the local distribution.

Thompson Lake carries an invasive watermilfoil record — boat-launch decontamination and shoreline care matter more here than at uninfested lakes. The state fisheries records do not list documented species for Thompson Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. 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.