Staff with the Colorado Parks and Wildlife are evaluating their next steps to eradicate zebra mussels from Highline Lake after discovering previous efforts weren’t successful.

“This is heartbreaking,” said Robert Walters, invasive species program manager. “We knew this was a possibility, but held out hope lowering lake levels to expose shoreline and the application of EarthTech QZ would effectively eradicate the zebra mussels that were discovered last fall.”

CPW staff found additional mussels at Highline Lake west of Grand Junction during routine work to remove buoys from the water in preparation for winter. Five adult zebra mussels were found on the bottom of buoys located throughout the lake. Additional work was scheduled to remove boat docks and two CPW boats. The docks and boats will be inspected for zebra mussels and decontaminated.

While a plan hasn’t been finalized, all options being considered likely will have significant implications for the fishery, boating and other water-based recreation at Highline Lake. They could include lowering or even draining the lake in 2024.

For now, an emergency fish salvage has been implemented. Bag and possession limits for the reservoir are removed for the duration of the salvage. Anglers can keep all of the fish they catch using lawful angling methods. All fish caught must be dead prior to leaving the lake. The fish salvage doesn’t include nearby Mack Mesa Lake, where fishing regulations remain in effect.

Zebra mussels were first discovered in Highline Lake in September 2022, prompting CPW to change the status of the lake from suspect to infested. It was the first time a body of water was categorized as infested with zebra mussels in Colorado.

Over the next several months, Highline Lake was lowered about 30 feet to expose areas along the shoreline to kill zebra mussels through the natural processes of desiccation and freezing. In March 2023, CPW applied three separate treatments of EarthTech QZ, an EPA-registered copper-based molluscicide to the lake.

“Eradicating invasive mussels is extremely difficult, which is why we focus so heavily on preventing their introduction,” Walters said. “While this is disappointing, we are not considering this first attempt a failure. We believe if we had done nothing, we would be looking at a much larger infestation today with fewer options for eradication and a greater chance of zebra mussels spreading to other bodies of water in Colorado.”