Zebra Mussels Detected at Sheridan Reservoir, Marking Second Infestation in Western South Dakota

A small zebra mussel rests on a person's palm, highlighting the invasive species campaign by SDLeastWanted.SD.gov and Northeast Radio SD to raise awareness.

Northeast Radio SD News – South Dakota - The South Dakota Game, Fish and Parks (GFP) is urging the public to inspect docks and equipment for zebra mussels as cooler temperatures prompt winter removal, following a recent positive detection at Sheridan Reservoir in the western part of the state.

The discovery makes Sheridan Lake the second waterbody in western South Dakota confirmed to have zebra mussels, following the confirmation at Pactola Reservoir in 2022.

Tanner Davis, GFP Aquatic Invasive Species Coordinator, emphasized the importance of late fall monitoring. "This is an important time of year for monitoring the spread of zebra mussels," Davis said. "Age-0 mussels, or those in their first year of growth, will be able to be detected on structures that have been placed in the water throughout the summer months."

Inspections Reveal Age-0 Mussels

The positive finding at Sheridan Reservoir came from inspections conducted by Rapid City fisheries staff, who detected two age-0 zebra mussels at separate locations within the reservoir.

The GFP has been working closely with the U.S. Fish and Wildlife Service, the U.S. Forest Service, and the Bureau of Reclamation to conduct watercraft inspections and monitor for invasive species.

In 2025 alone, staff performed 1,614 inspections at Sheridan Lake. Combined, 14,595 inspections were conducted across all five major West River reservoirs: Belle Fourche, Sheridan, Pactola, Angostura, and Shadehill, with staff operating 10 hours a day, 7 days a week.

Davis noted that this extensive effort is made possible by federal grants and partnerships with conservation districts in western South Dakota. However, he stressed, "While these inspections reduce the spread of zebra mussels, inspections are just one tool to slow the spread of aquatic invasive species."

Public Action Critical

As equipment removal continues across the state, the GFP is asking for assistance from private dock owners. Individuals are reminded to follow the Clean, Drain, Dry protocol every time they leave the water:

·         Clean all aquatic plants and mud from watercraft and trailers.

·         Drain all water, including pulling all boat plugs.

·         Dry equipment that has been submerged in water.

"If you find something you suspect is a zebra mussel or other AIS species, please submit a suspect report on the Citizen Monitoring page, contact your local or regional GFP office, or contact me directly at Tanner.Davis@state.sd.us," Davis concluded.