Thomson Reservoir

Thomson Reservoir grades an F: every scored parameter (clarity) rates poorly, placing it among the most stressed lakes monitored in Minnesota.

At a TSI of 61, Thomson Reservoir reads as eutrophic — nutrient-rich enough that summer algal growth and reduced clarity are expected, not unusual. A maximum depth of 22 ft puts Thomson Reservoir in the middle of Minnesota's depth distribution. The lake's 390 acres and 10.7 miles of shoreline put it in the mid-range bucket — large enough for varied use, small enough that watershed inputs reach the whole basin. Thomson Reservoir ranks 32 of 33 in Carlton County — at the lower end of the locally monitored distribution.

Thomson Reservoir has no invasive species recorded in Minnesota state databases as of 2021, though prevention practices still apply at all access points. Walleye are documented at Thomson Reservoir, one of 10 fish species on record for the lake. No formal public access is documented at Thomson Reservoir — 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.