A boat propeller clogged with mussels

A boat propeller clogged with mussels, an aquatic nuisance that can clog water infrastructure. Photo courtesy Colorado Parks and Wildlife.

An invasive adult zebra mussel was found on Sept. 14 in Highline Lake, just north of Fruita, prompting heightened monitoring and decontamination of boats.

The lake is part of Highline Lake State Park.

Wildlife officers found a single adult zebra mussel on PVC pipe in the lake during a routine invasive species sampling. It's the first adult mussel ever found in Colorado, according to the Colorado Parks and Wildlife.

Two CPW experts confirmed the mussel's identification. The mussel was also confirmed through genetics.

Colorado has so far escaped the kinds of mussel invasions that have plagued the Great Lakes region and states surrounding Colorado, including Texas, Arizona, Nebraska and Kansas.

Mussel larvae have been detected in eight different reservoirs in Colorado since 2008, according to CPW. The most recent was at Green Mountain Reservoir in Summit County in 2017, but that reservoir was declared mussel-free last year after three years of negative testing. The entire state was declared mussel-free in January, 2021.

According to the US Geological Survey, zebra mussels are an invasive, fingernail-sized mollusk. They are a native to the freshwaters in Eurasia. Their name comes from the "dark, zig-zagged stripes on each shell."

In the Great Lakes region, zebra mussels clog wastewater treatment systems, and result in millions of dollars in economic and environmental damage. In North America, the species have no known natural predators.

The mussel discovery prompted CPW to immediately increased monitoring at Highline Lake for all life stages of invasive mussels. That includes inspection and decontamination of boats launching at the lake. Boaters who plan to return to Highline Lake will be issued a green seal and blue receipt that indicates the boat was last used on a body of water with a known aquatic nuisance species, the CPW statement said. 

If a boater leaving Highline Lake intends to launch in a different water body, a certified professional must decontaminate the boat first. 

Highline Lake closes to all surface-water activities annually on October 1.

"We know this is an extra step for those who have come out to enjoy recreating on the lake, but staying vigilant has proven to be effective throughout Colorado," said CPW Northwest Region Manager Travis Black.

CPW's Invasive Special Program Manager Robert Walters added that, "although this is very troubling, it's important to keep in mind that the lake is not considered infested."

Walters said that designation is given to bodies of water that have "extensive and reproducing adult populations." He noted that, at this point, CPW detected only a single invasive mussel at Highline.

"We will continue to monitor throughout the fall to get a more complete picture of the species’ presence in the reservoir," he said.  

The state ramped up its invasive mussel program in 2018 through passage of the Mussel Free Colorado Act by the General Assembly.

The program requires all boat owners, whether Colorado residents or from out-of-state, to have an aquatic nuisance species (ANS) tag prior to launching in any Colorado lake. The tag, which is $25 for Colorado residents and $50 for out-of-state visitors, pays for the state's watercraft inspection and decontamination prevention system.