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This undated photo provided by the U.S. Department of Agriculture shows a group of zebra mussels. The invasive species of small mollusks is growing in Colorado. Federal officials have offered a $100,000 prize in a crowdsourcing effort to find a way to kill invasive quagga and zebra mussels. (U.S. Department of Agriculture via AP, File)

Invasive zebra mussels have “infested” the water at Highline Lake — a reservoir north of Loma, near Utah — despite a 15-year effort by Colorado Parks and Wildlife to keep the state free of the harmful species, the agency said this week.

CPW staff have discovered at least 10 zebra mussels in Highline Lake.

After the first adult zebra mussel was found in the reservoir Sept. 14, Parks and Wildlife staff found almost a dozen more of the mussels in the same body of water on Friday and Sunday. Soon after, the department changed the status of the lake from “suspect” to “infested,” according to a news release sent Tuesday.

The new infestation could lead to millions of dollars in damage to water-based infrastructure, and threatens to impact water quality and limit recreational opportunity. 

A single mussel can produce up to 1 million babies in a single year, officials said, making it challenging to contain the species, and nearly impossible to eradicate them once they’re introduced.

The aquatic nuisances attach to solid or semi-solid surfaces and clog up boat engines or distribution pipes at water treatment facilities. If knocked off, the mussels can drop into and infest a body of water.

A heavily infested propeller and lower unit of a boat is pictured by Colorado Parks and Wildlife inspectors. The organization has since 2008 run an aquatic nuisance program that intercepts and decontaminated more boats each year in hopes of keeping invasive species out of Colorado’s waterways. (Provided by Robert Walters, Colorado Parks and Wildlife)

The mussels can live outside of water for 27 days under the right conditions, and can pass almost a liter of water through their shells each day, consuming nutrients needed by other fish and plants in the ecosystem.

Their high levels of filter feeding can also alter food sources in lakes and reservoirs. And when mussels defecate or dry out on shorelines, they can cause a rancid smell, making it less desirable for people to recreate in these areas, said Robert Walters, CPW’s invasive species program manager.

Now, the agency will have increased sampling and monitoring efforts at Highline Lake to help contain the infestation. They also have implemented a special program where they will inspect and decontaminate every boat that leaves the lake to stop the species from spreading to other bodies of water, he said.

“This is incredibly concerning,” Walters said Wednesday. CPW’s invasive species leaders are evaluating other steps to contain the mussels, he said.

There currently are no boats on Highline Lake, since the boating season ended Sept. 30, and so it is unlikely that the zebra mussels will be shuffled around by recreation, at this point, Walters said. 

Highline Lake, which is northwest of Grand Junction and just a few miles east of the Utah border, is considered “high risk” for the spreading of mussels from boats. Many boats pass through the lake from out of state, particularly from Lake Powell on the Utah-Arizona border, a popular destination for Colorado boaters. Lake Powell has been infested with invasive mussels since 2012.

Now that Highline Lake is considered infested, it must go five years without further detections to be listed as free of mussels. 

Colorado Parks and Wildlife leaders have been concerned for years about the possibility of zebra and quagga mussels popping up across the state. The department conducted an awareness campaign ahead of Memorial Day, when the boating season generally kicks off in Colorado, to encourage people to get their boats inspected each time they enter and exit Colorado’s waterways.

The department stepped up enforcement of its 15-year-old Aquatic Nuisance Species Program, a statewide decontamination program, where inspectors at 73 locations decontaminate people’s boats. Since the program’s inception in 2008, almost 500,000 boats have been inspected annually. Parks and Wildlife staff deploy instruments into high risk reservoirs for the purpose of detecting invasive species. Staff found the first zebra mussel in mid-September during this kind of water sampling. 

Colorado is not free of all invasive aquatic nuisance species. Some bodies of water in Colorado contain Eurasian watermilfoil, for example, which grows quickly and blocks sunlight, and can kill off native aquatic plants that fish and other underwater species rely on for food and shelter.

Now, after the new detection, CPW staff are asking people to help stem the spread of zebra mussels by ensuring that any boating equipment that enters Highline Lake, and any other body of water in the state, is clean, drained and dried, in between each use. Mussel infestations are increasing across the nation each year, Walters said.

“As more and more people use our water resources for boating, we must continue to work tirelessly to prevent the spread of these harmful invasive species,” said Heather Dugan, acting director for Colorado Parks and Wildlife.

For more information about zebra mussels, visit: https://cpw.state.co.us/aboutus/Pages/ISP-ANS.aspx 

Tatiana Flowers

Tatiana Flowers is the equity and general assignment beat reporter for the Colorado Sun. She has covered crime and courts plus education and health in Colorado, Connecticut, Israel...