Thomas Lake

On the LakeGrade rubric, Thomas Lake pulls an A: clarity at 49.2 ft and phosphorus readings still being added put it in the top bracket for Wisconsin. 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.

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 28 ft — a moderate depth that supports a warm-water fishery without the year-round cold refuge a deeper basin provides. Thomas Lake is small — 32 acres alongside partial shoreline records — which makes it sensitive to even modest changes in watershed runoff or recreational pressure. Within Portage County's 29 graded lakes, Thomas Lake ranks 18 — below the local median, though not at the bottom.

Eurasian watermilfoil has been documented at Thomas Lake, requiring shoreline management to keep dense mats from crowding native vegetation. The fishery is bass-led, with 4 documented species across the lake's records. Public access is available — the lake is on the Wisconsin DNR 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.