Officials were baffled by a surprise discovery in the Colorado River earlier this year, involving a destructive invasive species capable of causing significant damage to aquatic environments.
In early July, officials in Colorado reported the discovery of a population of mature Dreissena polymorpha, otherwise known as zebra mussels, in the Colorado River. These small, innocuous-looking freshwater mussels, bearing zigzag markings on their shells, are a major concern, as they can accumulate around areas where water passes, blocking its flow and causing other damaging effects on the surrounding environment, as well as on infrastructure and sailing vessels.
Since zebra mussels can quickly latch onto boats, it has been believed that these invasive mollusks would often make their way into Colorado by contaminating boats in other states, such as Arizona and Utah. Recreational boaters who visit Lake Powell, which has long been infested with these destructive mussels, were believed to be carrying the species with them when they brought their boats to Colorado.
However, officials with Colorado Parks and Wildlife (CPW) now say they have determined the likely origin of a population of zebra mussels found in the Colorado River on July 3, 2025.
A Potential Source is Identified
Speaking at a roundtable on July 28, Maddie Baker, who specializes in the study of invasive species with CPW, revealed that investigations had traced the likely source of these invasive pests to a small private lake located upstream.
The zebra mussels may have been able to contaminate several surrounding bodies of water, the Grand Junction, Colorado Daily Sentinel reported, including Highline and Mesa Lakes, and the Colorado River.
“We do believe this to be the primary source,” Baker said at the July meeting, “but it could now have created other secondary sources downstream with locations that hold water.”
Baker said that the apparent ability of these invasive mussels to travel from areas as distant as Eagle County into larger bodies of water in the state suggests the possibility of “some sort of intermediate population in between.”
“So we still have a lot to figure out,” Baker told meeting attendees.
Dangers to Colorado’s Waterways
Earlier this year, the CPW issued a warning to the public about the dangers invasive mussels present to Colorado’s waterways and surrounding infrastructure.
“CPW is leading the charge against these destructive species,” said Robert Walters, the program manager for CPW’s Aquatic Nuisance Species (ANS) operations.
“As the spring season approaches, we ask for help from both the boating and water-based recreation communities to combat invasive species in the state,” Walters said in April.
According to the CPW release, Colorado’s ANS inspectors had undertaken more than 460,000 inspections in 2024 alone, during which they successfully decontaminated 32,584 boats that had been suspected of harboring mussels or other aquatic invasive species.
During those decontamination efforts, 110 boats were confirmed to be carrying zebra mussles or other invasive varieties.
Along with potential sources in Utah and Arizona, several other nearby states, including Kansas, Nebraska, Oklahoma, Texas, and South Dakota, are known to have mussel infestations.
“Most Midwestern and East Coast states also have infested waters,” the CPW release stated.
Combatting Aquatic Nuisance Species
Compounding the problem is the fact that these invasive creatures can hitch a ride on virtually anything that gets wet—from aquatic vehicles used for recreation, to boots, equipment, and other objects that come into contact with contaminated waters.
As part of their efforts to curb the spread of these destructive aquatic pests, CPW began instituting cleaning stations for boats and other watercraft in various parts of the state, and began issuing advisories to the public on how to decontaminate their property and belongings to aid in the fight against further spread of ANS in Colorado’s waterways.
“Mussels aren’t going away,” the CPW release stated. “However, by continuing our preventative watercraft inspection program Colorado can continue to set an example in the West and keep our waters clear of highly destructive invasive species.”
Investigations Continue
As far as how the zebra mussels made their way into the private lake located upstream from the Colorado River, many questions remain. During CPW’s investigations, officials said they discovered evidence of shells along the shoreline, meaning that the zebra mussels infesting its waters must have made their way into the lake’s waters several years ago.
The location was discovered through a search using satellite imagery for lakes on private property. Afterward, CPW officials contacted the property owners and requested that they conduct inspections for the creatures.
The outlet where the mussels had apparently been exiting the lake and making their way into the Colorado River was identified and has since been addressed by CPW officials.
Still, questions remain about how the creatures made their way into the lake in the first place.
“The property owner is unsure of how this could have happened,” Baker said at the July 28 meeting, adding that the individual “is being cooperative” as CPW’s investigations continue.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. He can be reached by email at micah@thedebrief.org. Follow his work at micahhanks.com and on X: @MicahHanks.