Sybil Lake

Sybil Lake sits at the top of the Minnesota PCA grading rubric with an A, a mark reached by the cleanest lakes in Minnesota. With clarity and phosphorus scored, the sub-grades cluster within a letter of each other, pointing to stable conditions rather than one specific stressor.

The lake's low TSI puts it in oligotrophic territory — the cleanest of the four trophic classes, but also the most vulnerable to nutrient-driven shifts. The lake's 74 ft maximum depth is in the upper tier for Minnesota — deep enough for cold-water fish to find refuge in summer. Sybil Lake covers 683 acres alongside 9.2 miles of shoreline — a mid-sized water that supports a working fishery without being so large that conditions diverge between basins. Within Otter Tail County's 97 graded waters, Sybil Lake sits at rank 18, near the top of the local distribution.

Zebra mussels have been documented at Sybil Lake, which alters the filter-feeding balance and can paradoxically increase water clarity while disrupting the food web. Walleye are documented at Sybil Lake, one of 16 fish species on record for the lake. Public access is available — the lake is on the Minnesota PCA public-access list. The lake has a partial ice record — 20 observed ice-outs, centered near Apr 16. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.