Riley Purgatory Bluff Creek Watershed District (RPBCWD) staff discovered four adult zebra mussels in Lake Ann on July 12, 2023. They were found attached to a tree branch in shallow water near the public swimming beach on the south side of the lake.

A rapid response survey was conducted by RPBCWD, Carver County, and Minnesota DNR staff on July 14. Approximately six acres were surveyed in several areas of the lake in water up to 18 feet deep. Five additional adult zebra mussels were found attached to woody debris in the same location as the initial discovery. No zebra mussels were found in the other survey locations of the lake.

Because of the small number of zebra mussels found within an isolated area, a copper sulfate treatment is warranted to attempt control of the infestation. On Friday, August 4, a barrier will be installed around 0.69-acre and 0.34-acre areas on either side of the recreation dock.

On Monday, August 7, a licensed applicator will apply the copper sulfate treatment. No water use restrictions are associated with the treatment. Upon application, the water will have a slight blue tint, which should dissipate the same day. See map below for location of treatments as well as where the zebra mussels were found.