High Island Lake

On the LakeGrade rubric High Island Lake fails the cutoffs — a TSI of 73 and persistent algal pressure put it in the bottom tier. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

The hypereutrophic status — TSI 73 — reflects sustained heavy nutrient loading from the surrounding watershed and frequent algal pressure. High Island Lake is a shallow lake at 7 ft maximum depth, which means it warms quickly, mixes constantly, and amplifies nutrient inputs. At 1,340 acres, High Island Lake is one of the larger lakes in Sibley County, with 16.1 miles of shoreline supporting multiple distinct use patterns. High Island Lake ranks 2 of 2 in Sibley County — at the lower end of the locally monitored distribution.

High Island Lake has no invasive species recorded in Minnesota state databases as of 2025, though prevention practices still apply at all access points. The fishery includes walleye alongside the lake's other 11 documented species — a notable draw for Minnesota anglers. Public access is available — the lake is on the Minnesota PCA public-access list. Ice-out has been recorded 17 times at High Island Lake, with a median around Apr 3. 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.