Blackduck Lake

Blackduck Lake earns a C — middle-of-the-pack water quality, with one or two parameters dragging the average down from a stronger grade.

Mesotrophic conditions dominate at Blackduck Lake: enough nutrients for a healthy fishery, not so much that algal blooms become a chronic problem. A maximum depth of 30 ft puts Blackduck Lake in the middle of Minnesota's depth distribution. At 1,250 acres, Blackduck Lake is one of the larger lakes in St. Louis County, with 12.1 miles of shoreline supporting multiple distinct use patterns. Within St. Louis County's 187 graded lakes, Blackduck Lake ranks 106 — below the local median, though not at the bottom.

Blackduck Lake has no invasive species recorded in Minnesota state databases as of 2024, though prevention practices still apply at all access points. Walleye are documented at Blackduck Lake, one of 8 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. Ice-out has been recorded 12 times at Blackduck Lake, with a median around Apr 18. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.