Lake Jefferson

On the scoring rubric Lake Jefferson grades a D: clarity at 4.0 ft and phosphorus readings still being added keep it in the lower bracket for Le Sueur County. 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.

At a TSI of 57, Lake Jefferson reads as eutrophic — nutrient-rich enough that summer algal growth and reduced clarity are expected, not unusual. Lake Jefferson reaches 37 ft at its deepest point — typical for Minnesota mid-sized lakes, with seasonal stratification but limited cold-water refuge. The lake's 685 acres and 5.9 miles of shoreline put it in the mid-range bucket — large enough for varied use, small enough that watershed inputs reach the whole basin. Among the 16 graded lakes in Le Sueur County, Lake Jefferson sits at rank 6, above the county median.

Eurasian watermilfoil has been documented at Lake Jefferson, requiring shoreline management to keep dense mats from crowding native vegetation. The fishery includes walleye alongside the lake's other 18 documented species — a notable draw for Minnesota anglers. Public access is available — the lake is on the Minnesota PCA public-access list. 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.