Zebra mussels were discovered in the Colorado River and Government Highline Canal, Colorado Parks and Wildlife (CPW) announced.

With single detections in both waters, these locations are now considered suspect for the presence of zebra mussels. CPW initiated an invasive species rapid response plan. More sampling is underway to determine if the classification should be changed to positive — a designation following two or more subsequent sampling events detecting mussel veligers.

“This challenging discovery has ecological and economic impacts not only on the Grand Valley, but potential statewide impacts as well,” said CPW Director Jeff Davis “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.”

Zebra mussels pose ecological effects. The establishment of zebra mussels in the Colorado River is likely to hurt native fish populations due to their filter-feeding strategies that strip essential prey items, such as plankton, from the water. Slower-moving sections of the Colorado River — including pools, eddies and backwaters — are especially prone to invasion.

Zebra mussels also pose a risk to infrastructure that pulls water from the Colorado River. Female zebra mussels can produce up to 1 million eggs in a spawning season. As they mature, mussels bond to surfaces with byssal threads, making them extremely difficult to remove. This rapid reproduction coupled with their attachment by byssal threads can lead to clogged water infrastructures creating long-term maintenance issues.

On July 1, staff from the CPW aquatic nuisance species (ANS) team collected a plankton sample from the Government Highline Canal near Clifton. The sample was evaluated at the ANS lab in Denver, where a suspected single zebra mussel veliger was found. The sample was then sent to the CPW aquatic animal health lab for further analysis. On July 9, the lab notified Robert Walters, invasive species program manager, the sample was positive for zebra mussel DNA.

On July 8, CPW ANS staff collected plankton samples from two locations in the Colorado River upstream of the Grand Valley Water Users Canal diversion. On July 10, ANS technicians identified single suspect zebra mussel veligers in both samples. The samples were sent to the aquatic animal health lab for confirmation. On July 11, the lab confirmed the samples were positive for zebra mussel DNA.

A veliger is the free-floating larval stage of the mussel. At this stage of their life cycle, zebra mussels can only be seen under a microscope. No adult zebra mussels have been found at this time at either location.

“We are disappointed in the situation we find ourselves in,” said Ed Warner, area manager of the U.S. Bureau of Reclamation Western Colorado Area Office. “We know how much effort CPW has put into keeping the Colorado River clear of zebra mussels. This is an extremely difficult scenario for all who rely on the Upper Colorado River system. We look forward to partnering with CPW, our stakeholders and all involved to do what we can to address the situation.”

Tina Bergonzini, general manager of the Grand Valley Water Users Association, called the zebra mussel detection devastating. “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. Our efforts, alongside our partners at CPW and the BOR, will be increased to protect our infrastructure, the livelihoods of so many and water security for us all.”

CPW staff will continue working  the Bureau of Reclamation and Grand Valley Water Users Association on the next steps. Signs alerting the public of the river status will be posted at river access points from De Beque Canyon to the Loma Boat Ramp.

“Detecting mussels in the Colorado River highlights how critical it is for boaters, paddlers, anglers and any person recreating in Colorado’s waters to do their part in preventing the spread,” Walters said.

CPW 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.

CPW is evaluating options for the future management of Highline Lake based on this new information. Updates regarding access, fishing regulations and water management will be provided once those decisions have been made.

Colorado Parks and Wildlife drained Highline Lake west of Grand Junction as part of additional efforts to eradicate an infestation of zebra mussels there.