Voracious zebra mussels appear to be spreading into the Colorado River near Grand Junction and infesting the Government Highline canal watering Mesa County farms, less than two years after the invasive species first appeared in a Western Slope lake, wildlife officials said Tuesday.
Western Slope officials called the news “devastating,” and are warning downstream water conservation partners beginning with Utah that the fast-reproducing mussels are likely on the way. Colorado Parks and Wildlife had led the charge to combat zebra mussels after finding the first lake infestation at nearby Highline Lake State Park in September 2022.
The zebra mussels strip plankton from the water en masse, depriving native species of vital food. The females can produce a million eggs during a spawn, and masses of the growing mussels cling to docks, dams, intake valves and other river infrastructure, threatening damage in the seven-state Colorado River region serving 40 million people.
“This news is devastating,” Grand Valley Water Users Association general manager Tina Bergonzini said in a state release. “Having our canal and the Colorado River test positive increases the threat of this invasive species and could impact everyone in the Grand Valley. From irrigation to drinking water, the ramifications cannot be underestimated or overstated.” She said state and local partners will have to redouble efforts to hold zebra mussels out of new waters.
A zebra mussel veliger (larvae) discovered by CPW in the Colorado River near Grand Junction after routine testing in early July 2024 A veliger is the mussel’s free-floating (planktonic) larval stage that can only be seen under a microscope. (Source: Colorado Parks and Wildlife) Crews with Colorado Parks and Wildlife ready mussel-killing chemicals on the shore of Highline Lake near Loma on March 1. (Barton Glasser, Special to The Colorado Sun) Staff first found a zebra mussel larvae or “veliger” in a plankton sample taken July 1 at the Government Highline near Clifton. On July 8, CPW staff collected more plankton samples at two locations in the Colorado River above the Grand Valley Water Users Canal diversion. Those were positive for zebra mussel DNA as well, the state said.
The waters are now called “suspect” for zebra mussel presence, and will be moved into the “positive” category if more widespread testing continues to turn up the larvae. Adult mussels have not yet been found, with the larvae visible only under a microscope, the state said.
“This challenging discovery has ecological and economic impacts not only on the Grand Valley but potential statewide impacts as well. CPW is committed to working with all of our partners as we work to better understand the extent of this discovery and the next steps in protecting the natural resources and infrastructure,” Colorado Parks and Wildlife Director Jeff Davis said.
“We know how much effort CPW has put into keeping the Colorado River clear of zebra mussels,” said Ed Warner, area manager of the U.S. Bureau of Reclamation Western Colorado Area Office. “This is an extremely difficult scenario for all who rely on the Upper Colorado River system.”
Boaters, anglers and other river users must now help stop the spread, joining zebra mussel detection programs in other parts of Colorado and in Midwestern states overwhelmed by the creatures.
“CPW strongly encourages anyone boating, floating, paddling, or fishing in the Colorado River to clean, drain, and dry their vessels and equipment, including motorized boats, rafts, paddle boards, kayaks, and fishing gear after exiting the river,” a state release said.
The state had planned to drain Highline Lake, north of Loma near the Utah border, this year in an attempt to fight the mussels’ spread, but now must reevaluate, officials noted.
Highline Lake was considered “high risk” for the spread of mussels from boats. Many boats pass through the lake from out of state, particularly from Lake Powell on the Utah-Arizona border, a popular destination for Colorado boaters. Lake Powell has been infested with invasive mussels since 2012.
During its Highline Lake campaign, CPW stepped up enforcement of the 15-year-old Aquatic Nuisance Species Program, a statewide decontamination program that sends inspectors to 73 locations to treat boats for the mussels.
About 500,000 boats and other watercraft are inspected each year, with about 30,000 deemed a “high biological risk.” Of those, around 100 boats are found to be “fouled” by zebra mussels. The program also includes the kind of aggressive testing of vulnerable bodies of water like those conducted at Colorado River and Government Highline locations.
Michael Booth is a reporter for The Colorado Sun. His work frequently appears on-air at KUNC 91.5 FM and online at KUNC.org. Contact Michael at booth@coloradosun.com.
