Colorado Parks and Wildlife found a single zebra mussel larva in the Colorado River near New Castle in early June, the latest appearance of the invasive, fast-spreading nuisance in the river as it passes through western Colorado.
No adult zebra mussels have been found in the Colorado River. That’s good news for the river: Once adult populations are established, eradication is nearly impossible and can cost millions of dollars. Colorado Parks and Wildlife and its federal partners are still searching for the source of the zebra mussel larvae, called veligers.
Boaters, kayakers and those eager to play in Colorado’s lakes have a role in preventing the spread, especially during holiday weekends like the Fourth of July. They should make sure their watercraft are clean, drained and dry before entering any body of water, officials say.
“Although not ideal, these results provide us with critical information as we continue working closely with our partners to protect our natural resources and infrastructure crucial to the Western Slope, including our goal of identifying the source,” Robert Walters with Colorado Parks and Wildlife said in a press release on June 26.
On June 9, the Colorado Parks and Wildlife team collected plankton samples from several locations along the Colorado River between Glenwood Springs and Parachute.
On June 17, laboratory technicians identified a single suspected zebra mussel veliger in a sample collected near the Grand River Park in New Castle, dozens of miles upstream from where larvae were found in the Colorado River near Grand Junction in 2024. Two days later, test results showed the samples were positive for zebra mussel DNA, according to the news release.
The Colorado River flows southwest to supply water for about 40 million people across seven Western states and northern Mexico.
Zebra mussels are hungry, reproduce quickly and can ruin 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.
Female zebra mussels can each release a million eggs into bodies of water per year. Older zebra mussels have distinctive shells with a D-shaped, flat bottom and black-and-white zigzag stripes.
As many as 700,000 mussels can crowd onto a square meter. Well-established populations can clog up pipes and dam intakes, slowing or even stopping the flow of water to homes, farms and power plants.
They gobble up plankton, depriving native species of food. They can live outside of water for about 27 days under the right conditions. Decaying mussels stink up beaches and their broken shells can cut bare feet.
Temporary employees have completed 175,000 watercraft inspections this year, said Walters, who manages the state’s invasive species program.
“We have already intercepted 76 watercraft with invasive mussels on them,” he said, referring to either zebra mussels or their close (and similarly invasive) relatives, quagga mussels.
The Aquatic Nuisance Species team has collected 150 water samples since May from various locations in the Colorado River from Glenwood Springs to the Colorado-Utah border. They have collected 725 plankton samples statewide since April.
The New Castle larva is the first detection of a zebra mussel veliger in the Colorado River since the initial discovery of zebra mussels in the Government Highline Canal and Colorado River in July 2024.
The century-old Government Highline Canal, managed by the Grand Valley Water Users Association, is part of a system that delivers water to about 40,000 acres of cropland in western Colorado.
The canal intersects with the Colorado River northeast of Palisade at the red-roofed roller dam in DeBeque Canyon.
Colorado’s first adult zebra mussel appeared in 2022 in Highline Lake, a reservoir northwest of Grand Junction that also connects with the Government Highline Canal. Colorado Parks and Wildlife was forced to completely drain the lake in November to try to eradicate the mussels before refilling it this spring.
It is illegal to possess or cause invasive aquatic species to be released in Colorado, under a 2008 law, and boaters can face fines if they skip inspection stations during operating hours.
If officials find signs of mussels, they decontaminate motorized boats by spraying outside surfaces or flushing internal engine areas with 140-degree water (the temperature of warm coffee) that kills the mussels. No soaps or chemicals are used.
Boaters can also feel the sides of their equipment for signs of juvenile zebra mussels, called settlers, which feel like sandpaper that is difficult to remove.
Equipment typically has to stay in the water for a long time for mussels to attach. Boat slips and moored boats in marinas are at the highest risk.
Nonmotorized boats, like kayaks and paddleboards, are exempt from mandatory inspection because they pose less risk than trailers and motorized watercraft.
Low risk does not mean no risk, officials say. Colorado Parks and Wildlife’s website shares tips on how people should clean, drain and completely dry their gear after each use and before entering a body of water. Anglers can keep their gear free of mud and plants between each use.
The Aquatic Nuisance Species team, or ANS, has talked to about 2,900 people recreating with kayaks, canoes and other nonmotorized craft this year to educate them about invasive species and to do surveys.
If people see a possible sign of zebra mussels in the Colorado River, they should send photos to Colorado Parks and Wildlife at Invasive.Species@state.co.us.
