SIOUX FALLS, S.D. (KELO) – The Big Sioux River is now considered infested with zebra mussels, according to the South Dakota Game, Fish and Parks Department. 

On Thursday, the GFP said while conducting river otter surveys on the Big Sioux River, staff found zebra mussels at two locations. 

“The zebra mussels were detected roughly five miles south of Watertown, and downstream of the connected zebra mussel positive waterbody of Lake Kampeska,” Aquatic Invasive Species Coordinator Tanner Davis said in a news release. “In the fall, zebra mussels have attached to hard substances and can be easily detected, which is why we have included inspecting for zebra mussels in our fall sampling.”

The GFP says the Big Sioux River from Lake Kampeska to the Missouri RIver is now considered infested and high-profile signs will be placed on access areas. 

The Big Sioux River is the latest water body to become infested after zebra mussels were found at Roy Lake in Marshall County. 

Zebra mussels have been confirmed in more than a dozen South Dakota lakes including Lewis & Clark, McCook, Yankton, Sharpe, Francis Case, Pickerel, Cochrane, Kampeska, Dahme Quarry, Mitchell, Pactola, Enemy Swim, Blue Dog and South Rush.

In July, the James River was considered infested with zebra mussels. 

GFP Communications Manager Nick Harrington said fall is an important time of year for detecting zebra mussels. He encouraged people who believe they might have found a mussel on their boat, dock or lift to contact the local GFP office along with a photo and location of the suspect mussels. 

GFP officials want boaters to clean, drain and dry watercraft to help prevent the spread of zebra mussels.