St Croix Flowage Lake

St Croix Flowage Lake sits at the top of the Wisconsin DNR grading rubric with an A, a mark reached by the cleanest lakes in 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.

A TSI near 41 places St 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. The lake's surface area is not consistently recorded across state datasets — physical context remains partial. St Croix Flowage Lake ranks 17 of 40 in Douglas County — solidly in the upper half of the local distribution.

No invasive species are currently listed at St Croix Flowage Lake — the lake remains off the Wisconsin infested-waters roster. The state fisheries records do not list documented species for St 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.