Riley Purgatory Bluff Creek Watershed District (RPBCWS) 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.

RPBCWD, Carver County, and Minnesota DNR staff conducted a rapid response survey on July 14. Approximately six acres were surveyed in several lake areas 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 to control 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. The water will have a slight blue tint upon application, which should dissipate the same day. See the map below for the location of treatments and where the zebra mussels were found.

The presence of zebra mussels at Lake Ann will be closely monitored. 

Help Control the Spread of Zebra Mussels

1. Clean off  visible aquatic plants, animals, and mud from all equipment before leaving water access.
2. Drain watercraft bilge, livewell, motor, and other water containing devices before leaving water access.
3. Dry everything for at least five days or wipe with a towel before reuse.

RPBCWD monitors for zebra mussels by:

• Annual zebra mussel veliger sampling

• Semi-monthly boat launch scans

• eDNA testing

• Public access adult zebra mussel monitoring plate

• Carver County invasive species searching transects