Increased sampling efforts result in additional zebra mussel detections in Western Colorado

Rachael Gonzales
Northwest Region Public Information Officer
970-773-8587 / [email protected]
Twitter: @CPW_NW Increased sampling efforts result in additional zebra mussel detections in Western Colorado

GRAND JUNCTION, Colo. — On Thursday, July 3, Colorado Parks and Wildlife (CPW) Aquatic Nuisance Species (ANS) staff discovered a large number of adult zebra mussels in a privately owned body of water in western Eagle County. 

“This news is a direct result of increased sampling efforts, ” said CPW Director Jeff Davis. “This discovery is a significant step toward identifying a potential source of zebra mussels and advancing our efforts for eradication. It would not have been possible without the commitment to protect Colorado’s bodies of water by our Aquatic Nuisance Species staff.”

During the survey, staff discovered evidence of and collected samples of suspected adult zebra mussels in various locations. Visual identification of the samples was performed by ANS Staff and samples were sent to Aquatic Animal Health Lab (AAHL) for DNA confirmation. 

CPW staff is currently evaluating options for the next steps in eradicating zebra mussels from the body of water.

“Understanding the current extent of zebra mussels in western Colorado is a critical step in stopping their spread into new locations,” said CPW Invasive Species Program Manager Robert Walters. “Every new detection puts us one step closer to achieving this desired outcome.” 

CPW, in collaboration with our partners at the local, state and federal levels, will continue our increased sampling and monitoring efforts. We also appreciate the willingness of private businesses and individuals who allow our staff to access their properties to conduct surveys.

In addition to the discovery found in western Eagle County, CPW also identified additional zebra mussel veligers in the Colorado River near New Castle, Highline Lake and Mack Mesa Lake at Highline Lake State Park.

Colorado River
On July 3, CPW Aquatic Animal Health Lab (AAHL) confirmed three additional zebra mussel veligers in samples collected in the Colorado River between Glenwood Springs and Silt. Samples were collected on June 16 and taken to the ANS laboratory where the additional zebra mussels veligers were found. These samples were then sent to AAHL for DNA confirmation.

With the additional detections in sample results, the Colorado River is now considered "positive” for zebra mussels from the confluence of the Roaring Fork River to the Colorado-Utah border.

Since sampling efforts resumed in May, CPW has collected 225 water samples from various locations along the Colorado River, stretching from the headwaters in Grand County to the Colorado-Utah border. In addition to the samples from the Colorado River, ANS staff has collected 25 samples from the Eagle River and nine samples from the Roaring Fork River. There have been no detections of zebra mussel veligers in the samples from the Eagle and Roaring Fork rivers. To date, no adult zebra mussels have been detected in the Colorado, Eagle or Roaring Fork rivers. 

Highline Lake
On June 10, CPW ANS staff collected plankton samples from the patrol dock and inlet at Highline Lake as part of routine increased sampling efforts. ANS laboratory technicians identified one suspected zebra mussel veliger in each sample. The samples were sent to AAHL where they were genetically confirmed as zebra mussels.

“While we had maintained hope that our eradication efforts at Highline Lake would be successful, we have always known this was a lofty goal. This is the primary reason we have continued the implementation of the containment watercraft inspection and decontamination program at Highline Lake,” said Walters.

With Highline’s current designation as an infested body of water, boaters are reminded of the following protocols in place since 2023.

• Boats launching​ at Highline Lake will be subject to inspection and decontamination protocols before launching. 

• All boats must be clean, drained and dry before launching at Highline Lake, or they will be decontaminated.

• Upon exiting the lake, all boats will be inspected and decontaminated, and boaters will be issued a green seal and a blue receipt​ indicating the boat was last used on a body of water with a known aquatic nuisance species. 

Mack Mesa
On June 10, CPW ANS staff collected plankton samples in the area near the fishing pier at Mack Mesa Lake, located at Highline Lake State Park. ANS laboratory technicians identified one suspected zebra mussel veliger in the sample. The samples were sent to AAHL where the zebra mussel veliger was genetically confirmed.

On July 8, additional samples collected from Mack Mesa indicated additional zebra mussel veligers. With these additional detections, Mack Mesa is now considered "positive” for zebra mussels.

CPW is continuing to evaluate options for the future management of Highline Lake and Mack Mesa based on the latest sampling results.

Prevent the spread: Be a Pain in the ANS
Everyone has a part to play in preventing the introduction and spread of invasive species in Colorado. Simple actions like cleaning, draining and drying your motorized and hand-launched vessels — including paddleboards and kayaks — and angling gear after you leave the water can make a big difference to protect Colorado's waters.

Learn more about how you can prevent the spread of aquatic nuisance species and tips to properly clean, drain and dry your boating and fishing gear by visiting our website. Tips for anglers and a map of CPW’s new gear and watercraft cleaning stations are available here.

CPW also encourages those who use water pulled from the Colorado River and find any evidence of mussels or clams to send photos to [email protected] for identification. It is extremely important to accurately report the location in these reports for follow-up surveying.