Colorado Parks and Wildlife finds zebra mussel larvae in Colorado River and Government Highline Canal

Please see the following information from Colorado Parks and Wildlife concerning zebra mussel veligers found in the Colorado River and Government Highline Canal this month.

Colorado Parks and Wildlife (CPW) announces the discovery of zebra mussel veligers in the Colorado River and Government Highline Canal after routine testing in early July. 

On July 1, staff from CPW’s Aquatic Nuisance Species (ANS) team collected a plankton sample from the Government Highline Canal near Clifton. This sample was evaluated at the ANS Lab in Denver where a suspected single zebra mussel veliger was found. The Sample was then sent to CPW’s Aquatic Animal Health Lab (AAHL) for further analysis. On July 9, the lab notified Robert Walters, Invasive Species Program Manager, that 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 AAHL for confirmation. On July 11, the lab confirmed the samples were positive for zebra mussel DNA.

With single detections in both waters, these locations are now considered “suspect” for the presence of zebra mussels. In response to this detection, CPW has initiated their Invasive Species Rapid Response Plan and increased sampling is underway to determine if the classification should be changed to “positive," a designation given when two or more subsequent sampling events detect mussel veligers in a water body. 

A veliger is the free-floating (planktonic) 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.

“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,” said CPW Director Jeff Davis. 

Zebra mussels pose an extreme risk of ecological impacts to Colorado. The establishment of zebra mussels in the Colorado River is likely to negatively impact 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, such as 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 1,000,000 eggs in a spawning season. As they mature, the 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. 

“We are disappointed in the situation we find ourselves in,” said Ed Warner, Area Manager, BOR 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.”

"This news is devastating,” said Tina Bergonzini, Grand Valley Water Users Association General Manager “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 closely with our partners at 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 starting in the 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,” said Robert Walters, Invasive Species Program Manager. 

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. 

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.

Questions from the media for the Bureau of Reclamation can be directed to BOR Public Affairs Specialist Justyn Liff at 970-248-0625 or jliff@usbr.gov.

Questions from the media for the Grand Valley Water Users Association can be directed to GVWAU General Manager Tina Bergonzini at 970-242-5065 or tbergonzini@gvwua.com.

Read the CPW’s original release on their website.