Sullivan Lake

On the LakeGrade rubric, Sullivan Lake pulls an A: clarity at 10.8 ft and 14 µg/L of phosphorus put it in the top bracket for Minnesota. Clarity, phosphorus, and chlorophyll-a all rate similarly, so there is no obvious single lever to pull on watershed management.

The lake sits in the mesotrophic zone — the band where most well-managed Minnesota lakes fall. At 57 ft of maximum depth, Sullivan Lake stratifies reliably through the summer — the hypolimnion stays cooler and clearer than the surface layer suggests. With 1,103 acres of surface and 7.7 miles of shoreline, Sullivan Lake is a large water by Minnesota standards — recreational pressure is spread across a long shoreline. Among the 16 graded lakes in Morrison County, Sullivan Lake ranks 4 — in the top quartile locally.

No invasive species are currently listed at Sullivan Lake — the lake remains off the Minnesota infested-waters roster. The fishery includes walleye alongside the lake's other 18 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 logged at Sullivan Lake more than two dozen times, putting the median around Apr 19 — a useful baseline for tracking climate trends. The grade is based on limited monitoring — fewer than three independent measurement years contribute, so future updates may shift the letter.