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.

The Colorado Parks and Wildlife division, after three years of negative testing, has removed Green Mountain Reservoir in Summit County from the positive waters list for quagga mussels, a prohibited aquatic nuisance species.

Since the Summit County reservoir was the only body of water in the state suspected of having quagga mussels, "this de-listing makes Colorado a completely negative state for both zebra and quagga mussels," according to a CPW statement Monday. Regional standards require three years of subsequent negative testing in order to re-classify the water from Suspect to Negative.

Quagga mussel larvae were first detected in Green Mountain in August 2017. No adult mussels were ever found there or in any other body of water. 

However, in 2019, Colorado inspectors intercepted 51 boats, most coming from Lake Powell in Arizona, that were infested with the quagga mussel. 

"I am just being completely over-run by mussel-infested boats," said Robert Walters, CPW assistant manager for the ANS program. "We are having interceptions just about every day at waters throughout the state."

According to CPW, all boats not previously “sealed” at Colorado reservoirs receive a thorough inspection and engine flush at inspection stations. Any boats found with mussels must be completely decontaminated, a process that can last a week or more.

While the state has been on the lookout for aquatic nuisance species since their first sighting in 2008, the program was hit with budget cuts just as mussels and their larvae were increasingly being found on boats entering Colorado reservoirs. In 2018, the General Assembly passed the "Mussel Free Colorado Act," which set up new fees and fines to deal with the problem.

Boaters must now buy an Aquatic Nuisance Species stamp when registering a boat in Colorado. The stamp ​provides approximately half of the funding for the ANS Program operations annually, which includes watercraft inspection and decontamination services, monitoring of state waters and management of existing populations.

Related: Colorado lawmakers to recharge state program to contain aquatic nuisances

“After three years of negative testing, we are confident that Green Mountain Reservoir is free of invasive mussels and does not pose a risk to other aquatic resources,” Walters said in the Monday statement. “Colorado is the only state to de-list all mussel positive waters. This is a testament to the fact that our mandatory watercraft inspection and decontamination procedures do work to protect Colorado’s waters from invasive species.”

While Colorado is once again completely free of invasive mussels, the threat of zebra or quagga mussels entering Colorado from another infested state is still quite real, according to CPW. Boaters using infested waters must take extra care not to transport mussels across state lines and to comply with Colorado's mandatory inspection regulations.

“Our staff want to express our gratitude to the boaters who help keep Colorado’s waters safe from harmful invasive species. By participating in Cleaning, Draining and Drying your watercraft and gear between each and every use, we can continue to prevent the spread of invasive species,” said Walters.

Mussels have been a major problem in the United States since they were first detected in the Great Lakes in the 1980s. According to the US Geological Survey, quagga mussels have been detected in several Colorado waterways since 2008, including at Lake Pueblo and the Pueblo Reservoir, but those populations have since been destroyed. 

Last November, eight federal government agencies signed a memorandum of understanding to guide their response to invasive zebra mussels and quagga mussels in 19 Western states, including Colorado.

Related: Federal agencies sign invasive mussel agreement for Western states

In December, the national ANS Task Force approved Colorado's management plan to protect the state's waterways from invasive species. 

According to CPW's Reid DeWalt, the ANS management plan "includes a coordinated prevention plan to keep Colorado’s waters free of ANS and a rapid response strategy that is designed to quickly contain new populations that may establish. This aims to minimize negative impacts on human safety, our wildlife populations and our native ecosystems.”

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