Black Brook Flowage Lake

On the LakeGrade scale Black Brook Flowage Lake grades a B, with clarity at 10.5 ft and 47 µg/L of phosphorus placing it above the Wisconsin median. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

Eutrophic conditions are the baseline here: clarity drops noticeably in late summer, and dissolved oxygen near the bottom can become a concern. The lake bottoms out at 23 ft — a moderate depth that supports a warm-water fishery without the year-round cold refuge a deeper basin provides. The lake is compact at 69 acres, with partial shoreline records and little volume to buffer nutrient inputs. Among the 74 graded lakes in Polk County, Black Brook Flowage Lake sits at rank 33, above the county median.

Black Brook Flowage Lake has at least one documented invasive species (Banded Mystery Snail), so boaters and anglers should observe clean-drain-dry steps when leaving the lake. Bass fishing is part of the appeal: the species list runs to 4, anchored by largemouth and/or smallmouth bass. A documented public access point at Black Brook Flowage Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.