The Wyoming Game and Fish Department is increasing measures to screen for aquatic invasive species, following the detection of zebra mussels in a reservoir 27 miles from the state line.
The problematic mussels were discovered in the Pactola Reservoir near Rapid City, South Dakota, in mid-July. Their presence represents a threat to Wyoming’s water-based ecosystems, wildlife authorities say.
Zebra mussels are associated with multiple negative consequences, including adding competition for food sources, which can ultimately blight out native species. They pose a threat to water-based human infrastructure, such as dams, irrigation and power plants.
Zebra mussels are fingernail-sized mollusks with black-and-white striped shells. According to the U.S. Geological Survey, they were inadvertently brought to this country in the 1980s when large ships from Europe were transplanted onto the Great Lakes.
Since then, zebra mussels have spread rapidly throughout that region and the large rivers of the eastern Mississippi drainage zone. They have also been detected in Texas, Colorado, Utah, Nevada and California. Wyoming is one of the few states in the area yet to be affected.
North Dakota Game, Fish and Parks communications manager Nick Harrington said it was a tip from a member of the public that made his agency aware of the mussels in the Pactola Reservoir.
“There was a guy spear-fishing, and he noticed it was on his sunglasses,” he said. “From there, he let us know, and we did additional testing of the water, and there were additional samples that came up positive.”
Prior to the discovery at Pactola, North Dakota officials were aware of the presence of this species in at least two water bodies in the eastern part of their state. The recent discovery signals that the species has traveled much farther west, and it was undetected until it reached its adult life stage.
With that information at hand, Pactola Reservoir is now considered to be infested, and containing the spread will involve diligence of every outdoor recreator. Boaters must strictly adhere to “Clean, Drain and Dry” protocols.
Wyoming Game and Fish Department Aquatic Invasive Species Coordinator Josh Leonard said the discovery of an adult mussel so close to the Wyoming state line is extremely concerning.
“We haven’t had a mussel-positive water producing adults this close to Wyoming – ever,” he said, noting that outdoor recreators frequently bounce between waterways in close geographic proximity. “It’s less than an hour drive from that water to the Keyhole Reservoir. If there’s a boat coming off of the Pactola coming here, and it’s not inspected or decontaminated, the transmission probability is really high.”
According to Wyoming Game and Fish, zebra mussels can spread even in a microscopic form from a very small amount of standing water left on a watercraft.
The good news is a robust inspection program has been in place for years to prevent such an event from occurring. All who enter the state with a motorized watercraft are required to stop at one of the various inspection stations upon entry. If they do not pass such a station, they must seek out an individual inspector before launching into Wyoming waters.
Leonard said the news of an invasive species so close to Wyoming has prompted the department to increase the operating hours of existing boat inspection sites. There is also a renewed push to raise public awareness about what’s at stake.
“We have been able to hold our eastern border up to this point, and we are confident we can keep it that way,” Leonard said. “I think the program is well set up to do that. We may need to reevaluate some of the secondary highways that might need more attention looking forward. Still, we are optimistic we will be able to work together across both jurisdictions.”
Leonard said his department will also conduct more frequent sampling of Wyoming’s waterways. Typically, reservoirs in northeast Wyoming have been sampled for aquatic invasive species once or twice a year. Going forward, those same water bodies will be tested monthly.
“We are in this together, and we need boaters to comply with our ‘clean, drain and dry’ message,” Leonard said. “We can’t be out there all the time. Boaters and recreators are out there every day, and we are counting on them to do the right thing.”