Adult zebra mussels have been found in the Colorado River and a nearby lake in Grand Junction, Colorado Parks and Wildlife said Monday.
The agency has detected the invasive species in its larval stage, called a veliger, in past sampling efforts in the river and nearby lakes. This is the first time an adult zebra mussel, a sign of a more established population, has been found in the Colorado River in Colorado.
“While this is news we never wanted to hear, we knew this was a possibility since we began finding veligers in the river,” CPW Director Jeff Davis said in the news release. “I can’t reiterate this enough. It was because we have a group of individuals dedicated to protecting Colorado’s water resources that these detections were made.”
The agency’s Aquatic Nuisance Species program staff confirmed zebra mussel veligers in West and East Lake near Clifton on Aug. 28. During a follow-up survey Sept. 2, staff discovered suspected adult zebra mussels in the lake, located west of 31 Road within the wildlife area section of James M. Robb-Colorado River State Park, the news release said.
The team found additional suspect adult zebra mussels in a side channel, which connects the lake to the Colorado River, and in the Colorado River where the side channel meets the mainstem.
On Sept. 8, the Aquatic Animal Health Lab confirmed the samples collected are adult zebra mussels.
The Colorado River is now considered an “infested” body of water from the 32 Road bridge downstream to the Colorado-Utah border. The designation means it has an established population of an invasive species. In this case, multiple zebra mussel life stages, from veliger to adult.
Zebra mussels are hungry and reproduce quickly. They can take up key nutrients for other aquatic species — tanking food systems — and can build up in layers on docks, pipes and diversion headgates, ruining water infrastructure. They are already well established in parts of nearby states, including Texas, Utah and Nevada, the Great Lakes and the Mississippi River Basin. Officials found the first adult zebra mussel in Colorado in 2022.
In late August, CPW staff treated a privately owned body of water in western Eagle County with EarthTec QZ, an EPA-registered copper-based molluscicide. The state officials found a large population of adult zebra mussels in the lake in July.
“We won’t give up,” Robert Walters, CPW invasive species program manager, said in the news release. “Our priority remains utilizing containment, population management and education to protect the uninfested waters of the state.”
Where has the state found zebra mussels?
The following bodies of water have the designation of an “infested” body of water:
- Highline Lake at Highline Lake State Park (designated in 2022)
- Mack Mesa Lake at Highline Lake State Park (2025)
- West and East Lake at the Wildlife Area Section of James M. Robb-Colorado River State Park (2025)
- Colorado River from 32 Road bridge downstream to the Colorado-Utah border (2025)
- Private body of water in Eagle County (2025)
CPW is working to contain the infestation in Highline Lake, Mack Mesa Lake, and West and East Lake. The agency is not planning to treat the Colorado River because of risk to native fish populations and critical habitat, the length of the potential treatment area, and complexity of canals and ditches that are fed by the Colorado River, according to the news release.
Since mid-April, CPW has collected 427 water samples along the Colorado River. Of those, six samples contained zebra mussel veligers.
No zebra mussels have been found between the headwaters of the Colorado River near Grand Lake and where the Roaring Fork meets the Colorado River in Glenwood Springs.
The Aquatic Nuisance Species staff also collected 41 samples from the Eagle River and 42 samples from the Roaring Fork River, finding no veligers in the two tributaries to the Colorado River.
The Colorado River remains classified as “positive” for zebra mussel veligers from Glenwood Springs to 32 Road bridge in Clifton.