SIOUX FALLS, S.D. (KELO) – Jay Gilbertson wants to see more collaboration when it comes to the future impact zebra mussels may have on the City of Sioux Falls. 

Right now, zebra mussels are not confirmed in the Big Sioux River near Sioux Falls, but last week the South Dakota Game, Fish and Parks Department classified the river from Watertown to the Missouri River as infested with the tiny snail-like mollusks. 

Gilbertson, the manager of East Dakota Water Development District, said he’d like to see a plan of when GFP would start looking for zebra mussels near Castlewood, Estelline, Brookings and Sioux Falls. 

“The presence of the zebra mussels may well be inevitable. That’s just the way it is,” Gilbertson told KELOLAND News. “Rather than sit back and just wait for it, let’s get out there and start planning. Let’s go out and start aggressively sampling at sites where we don’t. Let’s start making plans to get it ready for when they get down here.” 

When will zebra mussels get to Sioux Falls? GFP officials say that’s complicated to predict.

GFP Aquatic Invasive Species Coordinator Tanner Davis told KELOLAND News the only confirmed zebra mussels in the Big Sioux River were found five miles south of Watertown. He said it’s hard to predict when people would start seeing zebra mussels in Sioux Falls. 

“It’s very system dependent,” Davis said. “We’re going to continue to monitor the spread. We have folks out there removing infrastructures across the state as we speak.”   

Davis said zebra mussels move in larval stage, which happens in early summer months, and they free float for 2-3 weeks downstream. 

“I think we’re out of the woods for this year,” Davis said. “If we haven’t seen them yet this year, I don’t foresee them popping up downstream in these major cities in 2023.”

Zebra mussels at Pickerel Lake in August 2021.
Zebra mussels at Pickerel Lake in August 2021. Photo courtesy: Dan Loveland.

Despite the invasive species not expected to be in Sioux Falls this year, Gilbertson said planning should commence now for how to deal with them when they arrive. Gilbertson pointed out the City of Sioux Falls has a water intake system right where the Big Sioux River diversion channel starts in northern Sioux Falls.

According to a 2020 Sioux Falls Water Purification report, Big Sioux River surface water accounted for 266.22 million gallons of water treated by the plant for public consumption. 

In 2020, surface water from the Big Sioux River made up 6.3% of the water treated in Sioux Falls, but it was as high as 15% in 2022. 

The City of Sioux Falls also gets 17 million gallons of water a day from the Lewis and Clark Regional Water System. Gilbertson said if the city loses some of its surface water production from the Big Sioux River, there’s no more options from Big Sioux River aquifers.

Ryan Johnson, a Public Works Utility Administrator with the City of Sioux Falls, said the spread of zebra mussels isn’t known to have reached Sioux Falls yet.

“The City of Sioux Falls takes the protection of our water supply and water infrastructure seriously and will continuously monitor our infrastructure as well as monitor the spread with our partners at the GFP,” Johnson said in an emailed statement. “Should infestation occur near Sioux Falls, there are a variety of technologies available to address the situation, some of which are already in place.”

Davis said there’s been no impacts in Sioux Falls yet, but conversations will happen over the winter to figure out the best management strategy.

Gilbertson said there’s plenty of examples of pictures of pipes that used to be 12, 15 or 20 inches in diameter that are packed with zebra mussels. 

“Some water will still move through but not very much,” Gilbertson said. “Something will have to be done. If the intake pipe starts to show evidence of colonies forming, are they going to have to go out and scrape it once a month, once a week? Are there chemical treatments? If so, is our system designed to accept that treatment system?” 

At Gavins Point dam in Yankton, the US Army Corps of Engineers installed an ultraviolet light system to kill mussel larvae floating through the system. Between 2014 and 2018, 2,500 man-hours were spent related to mussel issues impacting dam infrastructure, a news release from the Army Corps of Engineers said

Davis says the GF&P will be taking steps to reduce the spread, including removing water structures that the mussels can attach to. He says the public can also help stop the spread.

“With Zebra Mussels, they are very invasive, especially when they do establish themselves in a system. So continuing to practice, clean, drain dry is the most important thing that we can do,” Davis said.

Game, Fish and Parks says if you find a zebra mussel, leave it alone, snap a photo and log the location on the GFP Website.