Saint Croix Flowage Lake

On the LakeGrade scale Saint Croix Flowage Lake grades a B, with clarity at 10.5 ft and 24 µg/L of phosphorus placing it above the Wisconsin median. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

A TSI near 47 places Saint Croix Flowage Lake in the mesotrophic band — moderate productivity, with seasonal swings between clearer spring water and richer late-summer conditions. The lake's maximum depth is not yet documented in state morphometric records — context for its physical structure remains limited. Saint Croix Flowage Lake covers 1,913 acres alongside partial shoreline records, large enough that conditions can vary meaningfully between bays. Saint Croix Flowage Lake ranks 12 of 44 in Douglas County — solidly in the upper half of the local distribution.

Saint Croix Flowage Lake has no invasive species recorded in Wisconsin state databases as of 2020, though prevention practices still apply at all access points. The state fisheries records do not list documented species for Saint Croix Flowage Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.