Colorado Parks and Wildlife found a single zebra mussel veliger in the Grand River Park near New Castle. This is the first new detection of the invasive species since they were found in the Colorado River system in July 2024. 

Robert Walters, the agency’s invasive species program manager, said in a news release that while the discovery was “not ideal,” it provides Parks and Wildlife with “critical information” needed to guard the region’s natural and built resources and identify the source of the invasive species. 

Zebra mussels are known for their rapid reproduction rate and the extreme economic impact they can have. The invasive species can clog water infrastructure as well as alter habitat and wipe out essential prey for Colorado’s other fish species. 

The 2024 discovery prompted Parks and Wildlife to deploy an Invasive Species Rapid Response Plan, which included increased sampling efforts on the Colorado River from Glenwood Springs to the Utah border. Last year, the state wildlife agency and partners took over 350 samples from July to September during weekly sampling between De Beque and Grand Junction and on two multi-day rafting trips between Glenwood and Grand Junction. No additional zebra mussels were found. 

In May, Parks and Wildlife restarted its sampling in the region, taking over 150 samples along the same section of the Colorado River. 

The positive sample — a single zebra mussel veliger — was found in mid-June at the Grand River Park along the Colorado River in New Castle. 

Despite the hundreds of samples along the river and watershed, the agency has yet to find any adult zebra mussels, only the species’ free-floating larvae, known as veligers.

As sampling continues and Parks and Wildlife continues to locate the source of the veligers, it is also working to educate water users and boaters on how to prevent against contamination of these invasive mussels.

This includes clearing, draining, and drying all water vessels and gear — including fishing gear, motorized and hand-launched vessels like paddleboards and kayaks — after each use. This can prevent the introduction and spread of not only zebra mussels, but also other invasive aquatic species, according to Parks and Wildlife. 

Parks and Wildlife has installed new gear and watercraft clearing stations at popular recreation sites across the state, including near Basalt, Glenwood Springs, Grand Junction, Hayden, Steamboat Springs, and more.

“By cleaning, draining and drying your angling gear, you can avoid unknowingly moving an invasive species from one body of water to another or even between different stretches of the same river, which can cause a domino effect of invasion with irreversible ecological damage,” the agency warns. 

Once the species are introduced to a body of water, they can be nearly impossible to remove, as evidenced by the years-long battle against zebra mussels in Highline Lake.

The first adult zebra mussel was found in the lake — which is fed by the Government Highline Canal and connected to the Colorado River — in 2022. After finding additional mussels, Parks and Wildlife made numerous attempts to eradicate the species, including applying molluscicide to the lake, water sampling, cleanup efforts, and ultimately, draining the lake entirely this past fall. The lake was refilled this spring and will continue to be monitored closely for the species.