Updated at 9:12 a.m. on Friday, Aug. 8, 2025.
Colorado Parks and Wildlife has confirmed plans to begin treating a body of water linked to the Colorado River for invasive zebra mussels. The announcement comes after the river officially tested positive last month.
CPW will begin to apply EarthTec QZ, an EPA-registered copper-based molluscicide, to a privately owned lake in western Eagle County connected to the river system that tested positive for the species. Following the initial treatment, staff will monitor the water to evaluate its effectiveness.
CPW staff will continue sampling efforts on the Colorado River and its tributaries above and below the infested stretches of water.
“While the identification and treatment of this body of water is an important step forward for managing zebra mussels on the Western Slope, the fact is, we still don’t conclusively know if this is the only established population of zebra mussels in the Colorado River Basin or how these detections are related, ” said Invasive Species Program Manager Robert Walters.
Since efforts began in mid-April, CPW has collected 318 water samples from various locations in the Colorado River. Of those samples, CPW has confirmed four samples that contain zebra mussel veligers, or the larval state of the species, which are microscopic and can attach to any hard surface.
“As we have seen, eradicating invasive mussels is extremely difficult," Walters said. “That being said, the more confident we can be in our understanding of their current distribution, the better chance we have of effectively managing them. That is why we will continue our daily sampling efforts from the headwaters to the stateline.”
Learn more about how you can prevent the spread of aquatic nuisance species and tips to properly clean, drain and dry your boating and fishing gear by visiting our website.
Tips for anglers and a map of CPW’s new gear and watercraft cleaning stations are available here.
Editor's note: This story has been updated to clarify that a private body of water linked to the Colorado River will be treated for zebra mussels, not the river itself.
