Jacobs Lake

On the scoring rubric Jacobs Lake grades a D: clarity at 4.5 ft and phosphorus readings still being added keep it in the lower bracket for St. Louis County. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

A TSI in the eutrophic range signals a lake doing what nutrient-loaded waters do — supporting an active algal community at the cost of clear water. Jacobs Lake is a shallow lake at 9 ft maximum depth, which means it warms quickly, mixes constantly, and amplifies nutrient inputs. The lake is compact at 90 acres, with 2.6 miles of shoreline and little volume to buffer nutrient inputs. Within the 187 graded lakes of St. Louis County, Jacobs Lake sits at rank 169, near the bottom of the county list.

Jacobs Lake has no invasive species recorded in Minnesota state databases as of 2020, though prevention practices still apply at all access points. The state fisheries records do not list documented species for Jacobs Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. No formal public access is documented at Jacobs Lake — most use is by shoreline residents and their guests. The lake has a partial ice record — 19 observed ice-outs, centered near Apr 29. Monitoring depth is thin here: the LakeGrade rubric is applied to a small number of sample years, and the grade will be revised as more data accumulates.