Concerned about the ever-increasing possibility that noxious zebra and quagga mussels reach Wyoming waters, Rep. Don Burkhart (R-Rawlins) floated a pretty radical idea. 

“Should we consider just prohibiting nonresident boats in Wyoming?” the Carbon County lawmaker asked last week at the Wyoming Legislature’s Joint Travel, Wildlife and Cultural Resources Committee meeting in Cheyenne.

The question was directed at Wyoming Game and Fish Department Director Brian Nesvik, who clarified that fisheries managers have had those types of discussions. 

“I don’t know that the threat is to that level,” Nesvik said. “We haven’t got to the point yet where we’d recommend that — that’d be a nuclear option, for sure. It would impact a lot of folks. It would impact a lot of communities.” 

During the same informational conversation, Game and Fish’s fisheries chief, Alan Osterland, made it clear that the likelihood of the invasive species of Eurasian freshwater mussels reaching the Equality State just keeps increasing.

“Our two major threats have been the Colorado, with quagga [mussels], and then the mainstem of the Missouri, with zebra mussels,” Osterland said. 

Quagga mussels attach to a boat’s propeller in this photo from outside Yellowstone National Park. The invasive mussels are most commonly introduced into other ecosystems by motorized boats. (National Park Service)

Quagga and zebra mussels are so prolific and can get so dense they suffocate substrate and infrastructure: In the Great Lakes, quaggas have been counted at densities up to nearly 8,000 mussels per square meter. Mussel-encrusted lake bottoms not only squeeze out native mussels and arthropods, they filter water at high rates that remove nutrients and alter the foodchain in ways that can harm and even devastate sport fisheries. 

Now, those two concerning species are encroaching on Wyoming from every side except the north. 

The threat of zebra mussels along the east border heightened in summer 2022, when the first discovery was marked in the Black Hills just 28 miles from Wyoming in Pactola Reservoir. Previously, the closest recorded report was in the Missouri River basin below central South Dakota. 

In September the Idaho State Department of Agriculture sent out word that juvenile quagga mussels called veligers had been found in the Snake River below Twin Falls — the species’ first known occurrence in the Columbia River Basin. Five of the six states bordering Wyoming now contain populations of quagga or zebra mussels, with only Montana still clear of contamination. 

“I’m a realistic person,” Game and Fish Statewide Aquatic Invasive Species Coordinator Josh Leonard told WyoFile. “What we’re doing is staving something that may be inevitable, but I still hope that we can keep them out with the work we’re doing.” 

Some of the preventative work is out of Wyoming officials’ control. 

While testifying, Osterland called Idaho’s response to the Snake River discovery “pretty impressive.” Within weeks of the discovery, the state applied a copper-based pesticide to six miles of the Snake in an attempt to to decimate the newfound quagga mussels. Last year the fisheries chief was much less laudatory of South Dakota’s response, telling lawmakers he found it “hands off.” 

The Wyoming Game and Fish Department expends roughly $2.5 million annually guarding against the spread of aquatic invasive species. Boat checkpoints, mapped out here, are the backbone of the prevention program. (Wyoming Game and Fish Department)

Wyoming, meanwhile, has ramped up the preventative work that’s within its control. The state brought on two new mandatory boat checkpoints in northeast Wyoming, one near Newcastle and another near Manville, in response to zebra mussels’ spread into Pactola Reservoir. That was after staffing and closing down boat ramps at night at high-risk Keyhole and Glendo reservoirs during 2022 until each impoundment iced up. 

Statewide boat inspections also continue to pick up. Roughly 40,000 vessels would get checked annually about a decade ago, but the last three years in-state inspections have vacillated between roughly 65,000 and 75,000. And high-risk inspections — those of boats that came off known infected waters — have skyrocketed, increasing from about 1,500 a decade ago to more than 6,000 boats checked in 2022. So have the number of mussel-infested boat checks. That figure jumped from 15 in 2013 to 58 during 2022. 

Numbers of boats checked within Wyoming that were last launched on mussel-infected waters continues to climb. (Wyoming Game and Fish Department)

That all runs up a big bill. Wyoming Game and Fish, Osterland said, is now putting about $2.5 million toward its aquatic invasive species prevention work. For Leonard, the aquatic invasive species coordinator, it’s a worthwhile investment.

“We are spending a fair amount of money on prevention, but in reality it’s very minimal,” he said. “I think it’s really hard for some people to grasp and conceptualize what the impact is until it actually happens.” 

From damage to water conveyance infrastructure and other resources, the Montana Invasive Species Council once estimated $234 million in economic impacts if zebra and quagga mussels reach Montana waterways.

Meantime, Burkhart, the Rawlins representative, remains worried that one bad actor could ruin Wyoming’s zebra and quagga mussel-free streak. 

“Frankly, I think we’re playing with fire,” he said. “We’ve got a can of gasoline in one hand and a flare in the other. It’s just a matter of time.”

Mike Koshmrl reports on Wyoming's wildlife and natural resources. Prior to joining WyoFile, he spent nearly a decade covering the Greater Yellowstone Ecosystem’s wild places and creatures for the Jackson...

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  1. Our advantage is that we’re upstream from everyone else and these mussels cannot swim upstream. The only way they can arrive here is if someone brings them in. We are the headwaters to three major river basins. If we get them everybody will get them.

    1. Zebra Mussels don’t technically swim they just go with flow but the main way they get around is by attaching themselves to pretty much anything especially to boats so being upstream offers very little protection.

  2. If Wyoming is really determined to prevent invasive mussels in our waters a nuclear option should be considered now. Some of the actions could be banning felt soles on fishing boots and the confiscation of any boat entering the state which has not stopped at its first opportunity for inspection. This would include Wyoming boats returning to the state after leaving. The proceeds of the sale of confiscated boats could then be used to increase enforcement.

  3. My husband and I work at a Idaho boat Check station.
    Our opinion is
    Every boat owner is or should be our 1st line of defense. It’s there boat and ownership should require training on inspections. 0

    1. You are right with boat owners but but their are too many people who don’t care about anything just look at the trash along the sides of the highways and roads .

  4. As a former 22 year Wyoming resident and currently a AIS(Aquatic Invasive Species) boat inspector here in Vermont I just wanted mention that 1 female Zebra Mussel produces 1m eggs per season. They are already here but we have kept them in just Lake Champlain and not anywhere else….so far. Good luck!