Harpt Lake

The LakeGrade rubric puts Harpt Lake at a C: clarity at 3.5 ft, 44 µg/L of phosphorus, and a TSI of 59 signal an intermediate trophic state. With clarity and phosphorus scored, the sub-grades cluster within a letter of each other, pointing to stable conditions rather than one specific stressor.

At a TSI of 59, Harpt Lake reads as eutrophic — nutrient-rich enough that summer algal growth and reduced clarity are expected, not unusual. The lake's 54 ft maximum depth is in the upper tier for Wisconsin — deep enough for cold-water fish to find refuge in summer. The lake is compact at 32 acres, with partial shoreline records and little volume to buffer nutrient inputs. Within Manitowoc County's 18 graded lakes, Harpt Lake ranks 13 — below the local median, though not at the bottom.

Harpt Lake carries an invasive watermilfoil record — boat-launch decontamination and shoreline care matter more here than at uninfested lakes. The fishery includes walleye among the lake's 4 documented species — a notable draw for Wisconsin anglers. 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.