Colorado River Designated Infested With Zebra Mussels From Eagle River to Utah Border
Colorado Parks and Wildlife has confirmed zebra mussel infestation throughout a 200-mile stretch of the Colorado River following multi-agency sampling that discovered adult specimens near Rifle and in Glenwood Canyon.
The confirmation expands the designated infested zone to include the entire Colorado River from the Eagle River confluence downstream to the Colorado-Utah border. More than 70 people from nine agencies conducted the October 29 survey, sampling approximately 200 locations across 200 miles of the Colorado, Eagle, Roaring Fork and Gunnison rivers.
CPW discovered a single adult zebra mussel near Rifle during the large-scale effort. Follow-up surveys by Aquatic Nuisance Species staff found additional adult zebra mussels within Glenwood Canyon.
No zebra mussels have been detected upstream of the Eagle River confluence, according to CPW.
First Adult Specimens Found in September
Adult zebra mussels were first confirmed in the Colorado River mainstem in September 2024, marking an escalation from earlier detections of microscopic veliger larvae. CPW detected veligers in the river near New Castle in 2023, followed by adult specimens in a private Eagle County reservoir in July 2024.
The progression from veliger detection to adult populations indicates zebra mussels have established reproducing colonies in the river system. Adult mussels attach to hard surfaces in dense clusters, clogging water intake pipes, irrigation infrastructure and hydroelectric facilities.
"Although it is disappointing to have found additional zebra mussels in the Colorado River, this survey achieved its primary objective of gaining a more comprehensive understanding of the extent of the zebra mussel population in western Colorado," said Robert Walters, CPW's Invasive Species Program Manager.
Zebra mussels threaten Colorado's water infrastructure, with documented costs in other western states ranging from $3.5 million to $5 million annually for inspection, cleaning and mechanical removal at large water facilities, according to U.S. Bureau of Reclamation reports.
New Zealand Mudsnails Confirmed in Roaring Fork River
The survey also confirmed the first detection of New Zealand mudsnails in the Roaring Fork River. The invasive aquatic snail had previously been identified in the Colorado, Gunnison and Eagle rivers but not in the Roaring Fork drainage.
New Zealand mudsnails reproduce rapidly and can reach densities exceeding 500,000 per square meter, competing with native insects for food and disrupting aquatic food webs. The snails threaten trout populations by reducing available invertebrate prey.
CPW confirmed no zebra mussels or New Zealand mudsnails in tributary surveys of the Eagle and Roaring Fork rivers during the October effort. The Gunnison River survey near its Colorado River confluence also found no zebra mussels.
Teams divided the four rivers into sections to identify potential zebra mussel habitat and maximize survey coverage. Volunteers conducted shoreline inspections at approximately 200 locations, examining rocks and hard surfaces where zebra mussels attach.
Multi-Agency Partnership Enables Large-Scale Survey
Partner agencies participating in the October 29 sampling included the U.S. Fish and Wildlife Service, Bureau of Reclamation, City of Grand Junction, Eagle County, Mesa County, Orchard Mesa Irrigation District, Roaring Fork Conservancy and Utah Department of Natural Resources.
"We could not have pulled off such a massive effort without our partners," Walters said. "These partnerships are instrumental in the continued protection of Colorado's aquatic resources and infrastructure from invasive mussels."
The survey focused on western slope rivers that supply municipal water, support agriculture through irrigation systems and generate hydroelectric power. Zebra mussel blockages can reduce flow capacity in canals, force shutdowns of water treatment facilities and damage turbine cooling systems.
Grand Valley Project irrigation canals and diversion structures, which source directly from the Colorado River, face particular risk from zebra mussel colonization. Blockages could delay water deliveries during irrigation season and complicate Colorado River Compact allocation requirements.
CPW established its Aquatic Nuisance Species program in 2007 following quagga mussel detections in Lake Mead. The agency operates mandatory inspection and decontamination stations at major reservoirs statewide, including Northern Colorado waters that receive Colorado River water through the Colorado-Big Thompson Project.
Private Pond and Lake Owners Urged to Request Sampling
CPW is requesting public assistance to understand the full extent of zebra mussel presence in western Colorado. Property owners with ponds or lakes using water from the Colorado River or Grand Junction area canal systems can request free sampling by CPW staff.
The agency also asks anyone using water from the Colorado River who finds evidence of mussels or clams to photograph specimens and report exact locations for follow-up surveying.
Requests for sampling and reports of suspected mussels should be submitted to [email protected].
CPW will continue sampling through Thanksgiving, focusing on smaller ponds in the Grand Valley.
Colorado law requires all watercraft to follow "Clean, Drain, Dry" protocols. Motorized boats must display an Aquatic Nuisance Species stamp and undergo inspection at state-managed waters. Violations can result in fines up to $5,000 under state statute.
More information about aquatic nuisance species prevention and locations of gear cleaning stations is available at cpw.state.co.us.