Photo courtesy of Colorado Parks & Wildlife
Colorado Parks and Wildlife has confirmed adult zebra mussels in the Colorado River near Grand Junction and in a nearby lake within James M. Robb Colorado River State Park. These findings follow months of stepped-up monitoring that began after larval mussels, called veligers, were detected earlier this year.
“While this is news we never wanted to hear, we knew this was a possibility since we began finding veligers in the river,” said CPW Director Jeff Davis. “It was because we have a group of individuals dedicated to protecting Colorado’s water resources that these detections were made.”
What was found
In late August, laboratory testing detected zebra mussel DNA in samples from West and East Lake, west of 31 Road at the park’s Wildlife Area.
A follow-up survey on Sept. 2 found suspected adults in the lake, then in the outlet side channel that feeds the Colorado River, and at the point where the side channel meets the mainstem.
On Sept. 8, Colorado Parks and Wildlife’s Aquatic Animal Health Lab confirmed the adult mussel identifications by DNA testing.
This is the first time adult zebra mussels have been documented in the Colorado River. Based on these detections, the river is now considered infested from the 32 Road bridge downstream to the Colorado-Utah state line.
What “infested” means
Photo courtesy of Colorado Parks & Wildlife
A water is labeled infested when an invasive species is established and reproducing, which is confirmed when multiple life stages are present. A positive designation means detections have occurred but an established population is not confirmed.
Infested waters as of 2025:
• Highline Lake, Highline Lake State Park, 2022
• Mack Mesa Lake, Highline Lake State Park, 2025
• West and East Lake, James M. Robb Colorado River State Park, 2025
• Colorado River, 32 Road bridge to the Colorado-Utah border, 2025
• Private water in Eagle County, 2025Positive, not infested: Colorado River from the Roaring Fork confluence upstream to the 32 Road bridge.
No detections to date: From the headwaters of the Colorado River to the Roaring Fork confluence.
What CPW is doing now
Colorado Parks and Wildlife and partner agencies are expanding sampling and monitoring from Grand County to the Utah line to understand the extent of the spread.
Since mid-April, CPW has collected 427 water samples from the Colorado River. Six have tested positive for zebra mussel veligers.
Additional monitoring on the Eagle River, 41 samples, and the Roaring Fork River, 42 samples, has produced no veliger detections.
CPW is evaluating future containment and mitigation at Highline Lake, Mack Mesa Lake, and West and East Lake.
CPW does not plan to chemically treat the mainstem Colorado River, due to risks to native fish and habitat, the length of river involved, and the complexity of canals and ditches connected to the system.
In Eagle County, CPW treated a private pond in late August with EarthTec QZ, a copper-based molluscicide registered by the EPA. Follow-up surveys in early September found dead adult mussels in multiple locations in that pond. Monitoring will continue to assess effectiveness.
“We will not give up,” said CPW Invasive Species Program Manager Robert Walters. “Our priority remains utilizing containment, population management, and education to protect the uninfested waters of the state.”
How you can help
Be a pain in the ANS. Every boater and angler can limit the spread of invasive mussels with a few simple habits.
Clean: Remove plants, mud, and debris from boats, trailers, paddles, waders, nets, anchors, and coolers.
Drain: Empty bilges, ballast, live wells, and any gear that holds water before you leave the site.
Dry: Allow boats and equipment to dry completely before launching in new waters. Follow posted decontamination guidance and use CPW cleaning stations when available.
Report what you see. If you use water pulled from the Colorado River or Grand Junction canal systems and find shells or suspect mussels or clams, take clear photos and email them with precise location details to Invasive.Species@state.co.us.
Pond and lake owners: If your pond or lake uses Colorado River or local canal water, CPW would like to inspect and sample your site. Request a visit by emailing Invasive.Species@state.co.us.
What comes next
Expect to see more crews on the river and adjacent lakes as CPW and partners expand shoreline searches, plankton tows, substrate checks, and decontamination demonstrations. The focus is twofold: limit further spread, and protect waters that remain free of zebra mussels.
Colorado’s rivers, reservoirs, and community water supplies depend on all of us. Clean, drain, and dry every time; report what you find; and encourage friends and family to do the same.
