Linn Lake

Linn Lake earns a D — measurements through 2024 show persistent nutrient pressure that limits clarity through the summer. 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. The lake bottoms out at 15 ft — a moderate depth that supports a warm-water fishery without the year-round cold refuge a deeper basin provides. Linn Lake covers 177 acres alongside 3.2 miles of shoreline — a mid-sized water that supports a working fishery without being so large that conditions diverge between basins. Linn Lake ranks 27 of 31 in Chisago County — at the lower end of the locally monitored distribution.

Eurasian watermilfoil is established at Linn Lake, which can dampen recreational access and pressure the native plant community. The state fisheries records do not list documented species for Linn Lake, which usually reflects a lack of formal fisheries survey work rather than an empty lake. The lake lacks a documented public access point, so visitor use is limited. The grade is supported by multiple sampling years from Minnesota PCA volunteers and partner agencies, giving the letter a reasonably stable foundation.