Blackduck Lake

The LakeGrade rubric puts Blackduck Lake at a C: clarity at 6.2 ft, 40 µg/L of phosphorus, and a TSI of 54 signal an intermediate trophic state. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

At a TSI of 54, Blackduck Lake reads as eutrophic — nutrient-rich enough that summer algal growth and reduced clarity are expected, not unusual. 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. Blackduck Lake covers 2,711 acres alongside 13.4 miles of shoreline, large enough that conditions can vary meaningfully between bays. Within the 86 graded lakes of Beltrami County, Blackduck Lake sits at rank 81, near the bottom of the county list.

Blackduck Lake is on the watch list for starry stonewort, an invasive macroalga that is difficult to control once established. Walleye are documented at Blackduck Lake, one of 16 fish species on record for the lake. A documented public access point at Blackduck Lake makes the lake usable for shore fishing, paddle craft, and trailered boats. The lake has a long ice-out record — 55 observations on file, with a median ice-out around Apr 23. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.