Thirteen Lake

Thirteen Lake comes in at a B on the grading rubric — a respectable showing for a Minnesota lake of its size and depth. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

The lake's low TSI puts it in oligotrophic territory — the cleanest of the four trophic classes, but also the most vulnerable to nutrient-driven shifts. The lake bottoms out at 17 ft — a moderate depth that supports a warm-water fishery without the year-round cold refuge a deeper basin provides. Thirteen Lake is small — 80 acres alongside 1.4 miles of shoreline — which makes it sensitive to even modest changes in watershed runoff or recreational pressure. Thirteen Lake ranks 58 of 187 in St. Louis County — solidly in the upper half of the local distribution.

Thirteen 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 Thirteen Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. No formal public access is documented at Thirteen 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.