Preston Lake

Preston Lake grades an F: water clarity, phosphorus, and chlorophyll-a all rate poorly, placing it among the most stressed lakes monitored in Minnesota. The three sub-grades — clarity, phosphorus, and chlorophyll-a — track close together, so no single parameter is dragging the average.

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. A maximum depth of just 11 ft means sediment-bound phosphorus releases back into the water column whenever wind stirs the bottom — a classic shallow-lake dynamic. At 655 acres, Preston Lake fits the Minnesota median for monitored lakes, with 5.4 miles of shoreline. Among the 2 graded lakes in Renville County, Preston Lake sits at rank 1, above the county median.

No invasive species are currently listed at Preston Lake — the lake remains off the Minnesota infested-waters roster. The fishery includes walleye alongside the lake's other 13 documented species — a notable draw for Minnesota anglers. Public access is available — the lake is on the Minnesota PCA public-access list. The grade is supported by multiple sampling years from Minnesota PCA volunteers and partner agencies, giving the letter a reasonably stable foundation.