The Colorado River is officially infested with invasive zebra mussels from the Colorado/Utah state line to the 32 Road Bridge in Grand Junction, according to Colorado Parks and Wildlife.
The invasive bivalve has its origins in Eastern Europe, and originally came to North America to the Great Lakes via shipping vessels in the St. Lawrence Seaway. Adult zebra mussels reproduce rapidly, and attach in mass quantities to water infrastructure like irrigation and drinking water systems. Their infestation has caused hundreds of millions of dollars in damages in the Great Lakes region.
CPW increased sampling for zebra mussels in 2022, after finding an adult zebra mussel in Highline Lake in Grand Junction. The agency considers a body of water “infested” when it has an established population of an invasive species. There are five bodies of water in the state that meet that criteria of zebra mussels, where multiple life stages of the bivalve have been found.
Those are Highline Lake, Mack Mesa Lake, West and East Lake at the Wildlife Area Section of James M. Robb - Colorado River State Park, and the Colorado River from 32 Road bridge downstream to the Colorado-Utah state line. A private body of water in Eagle County was also found to be infested.
Earlier this summer, CPW found a single veliger (the larval stage of the zebra mussel) in the Colorado River near New Castle, the furthest upstream the species had been detected.
Rachel Gonzales, the public information officer for CPW’s northwest region, said the river upstream of the Roaring Fork River’s confluence with the Colorado River is still considered uninfested.
“We’re not going to give up, right?” she said. “Our priority remains the same, we’re going to utilize that containment, population management, (and) education to protect uninfested waters.”
She said the agency will continue its sampling and monitoring programs for zebra mussels, which span from the Colorado River’s headwaters in Grand County all the way to the Utah state line.
There are some treatments that wildlife managers can use for established populations of invasive mollusks, like zebra mussels and their relatives the quagga mussels (which have been found in the Colorado River Basin, in Lake Powell and Lake Mead.)
CPW has had mixed results with molluscicides. In late August, staff did treatments on the private body of water in Eagle County with EarthTec QZ, an EPA-registered copper-based molluscicide. In September, surveys found dead zebra mussels around the water, and say they’re still monitoring to see if it’s effective.
“Unfortunately, it didn’t have the results we hoped for,” Gonzales said of additional treatments done with EarthTec QZ at Highline Lake.
She said CPW has no plans to treat the main stem of the Colorado River, partially for logistical reasons: the river is part of a very complicated system of ditches and canals in the Grand Valley. But Gonzales said there are other factors they need to consider.
“Zebra mussels are filter feeders, so they’re already taking away from the nutrients that our native fish depend on, and we don’t want to put something else in the river that can further impact that,” she said. “We've got some endangered and threatened species within the Colorado River, we want to do what we can to protect those.”
She says as fall approaches, recreators will move away from boating and towards angling and water fowl hunting, and CPW is working on outreach to make sure those people clean, drain, and dry their gear to prevent the spread. There are cleaning stations near water bodies across the state.
Copyright 2025 Rocky Mountain Community Radio. This story was shared via Rocky Mountain Community Radio, a network of public media stations in Colorado, Wyoming, Utah, and New Mexico, including Aspen Public Radio.
