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Crews with Colorado Parks and Wildlife ready mussel-killing chemicals on the shore of Highline Lake near Loma on March 1. (Barton Glasser, Special to The Colorado Sun)

Colorado Parks and Wildlife staff have a new plan to eradicate invasive zebra mussels from Highline Lake — a reservoir north of Loma, near Utah – one year after the first adult mussel was found there.

The first phase will start this year and the second part will take place gradually throughout 2024, Colorado Parks and Wildlife staff said in a statement Thursday.

During the first phase, Parks and Wildlife staff will apply a higher concentration of EarthTec QZ, the same copper-based molluscicide that was applied to the lake in March. The chemical should help to suppress the mussel population and stunt their reproductive ability in 2024.

“We did not make this decision lightly or in haste,” Colorado Parks and Wildlife Invasive Species Program Manager Robert Walters said. “Over the past year we have had numerous discussions with CPW’s Northwest Region aquatic, regional, and state park staff and we have come up with a plan that builds upon that work that was performed last spring.”

In early 2024, Colorado Parks and Wildlife officials will begin lowering Highline Lake with the goal of emptying it by the end of the year. 

As a result, the lake will be closed to motorized boating and may reopen some time in 2025, said Rachael Gonzales, northwest region public information officer for Colorado Parks and Wildlife.

This year during the boating season, from April 20 to Sept. 30, Gonzales said 2,776 motorized boats traveled on Highline Lake.

The agency is committed to rebuilding the Highline Lake fishery once the zebra mussel eradication project is complete, said Ben Felt, northwest region senior aquatic biologist for Colorado Parks and Wildlife.

Alan Martinez, Highline Lake state park manager, knows it’s not ideal for those who frequent the lake. 

“What we hope is that people see this and understand how serious this problem is, and that it can be avoided by simply cleaning, draining, and drying your boat or any equipment that comes in contact with the water in between each and every use,” he said.

Kayaks and paddleboards will be allowed on Highline Lake, a popular destination for many outdoor recreationists, but those can also help zebra mussels move around the lake. Parks and Wildlife staff want people to clean, drain and dry kayaks and paddleboards.

Colorado Parks and Wildlife officials are not able to move fish out of Highline Lake before draining the water because there’s a risk of moving around invasive mussels latched onto or inside of other fish. 

The only option, officials said, is to reduce fish loss by removing bag and possession limits until further notice. 

Crews with Colorado Parks and Wildlife ready mussel-killing chemicals on the shore of Highline Lake near Loma on March 1. Zebra mussels are an invasive species native to Eastern Europe. (Barton Glasser, Special to The Colorado Sun)

An emergency fish salvage is in place at the lake, Colorado Parks and Wildlife staff announced last week, meaning anglers can keep all the fish they catch from the shoreline as long as they’re fishing legally. 

“We’re trying to give anglers an opportunity to put the fish to good use,” Gonzales said last week.

The first adult zebra mussel was found in the reservoir on Sept. 14, 2022, while Colorado Parks and Wildlife staff were routinely testing for aquatic nuisance species in the lake. Parks officials found almost a dozen more mussels there the next month.

Five more adult zebra mussels were found Oct. 1 on the bottom of buoys.

The discovery was troubling, though not surprising. Parks and Wildlife staff have been working for 15 years to keep the state free of the nuisance species, which can cause millions of dollars of damage to water distribution systems.

The infestation could lead to millions of dollars in damage to water-based infrastructure, and can threaten water quality and limit recreational opportunity, Roberts said last year after the first few mussels were found.

A single mussel can produce up to 1 million babies a year, can live outside of water for 27 days and can pass almost a liter of water through their shells each day, consuming nutrients needed by other fish and plants, Roberts said.

“While the efforts in early 2023 did not achieve our ultimate goal of eradicating zebra mussels, we believe it helped to keep population numbers at a manageable level,” he said. 

Parks and Wildlife staff are hoping to reopen the lake during the 2025 boating season. “And that might be when we see significant reduction,” Gonzales said. “It will probably be a year.”

Tatiana Flowers is the equity and general assignment reporter for the Colorado Sun and her work is funded by a grant from the Colorado Trust. She has covered crime and courts plus education and health in Colorado, Connecticut, Israel and Morocco....