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Colorado lakes and reservoirs remain free of invasive mussels, but Colorado Parks and Wildlife reported that its statewide inspection program found more boats with mussel infestations in 2019.

CPW officials said in a press release that they are concerned about the increasing number of boats entering Colorado that need decontamination.

“Colorado remains free of adult zebra and quagga mussel reproducing populations, while some nearby Western states without mandatory inspection programs continue to detect infestations,” Elizabeth Brown, the agency’s invasive species program manager, said.

“Colorado has prevented the introduction of this invasive species due to diligent efforts of watercraft inspection and decontamination, early detection monitoring, education and enforcement efforts.”

Other states that have mussel infestations include Arizona, Utah, Kansas, South Dakota, North Dakota, Oklahoma, Texas and California.

Mussels can clog pipes and other infrastructure, cover docks, shorelines, rocks or any hard surface and can ruin powerboat engines.

Throughout the state last year, CPW conducted 481,543 boat inspections, 7,000 more than in 2018. A total of 22,947 boats, 281 with attached mussels, were decontaminated, compared with 19,111 in 2018.

The number of intercepted boats fully infested with mussels increased by 40 percent, from 51 in 2018 to 86 in 2019. In 2017, only 16 mussel-infested boats were intercepted.

Brown said she’s worried about the substantial increase in infested boats entering the state.

“This growth trend is directly related to the growing threat invasive mussels pose to Colorado’s water infrastructure, natural resources and outdoor recreation,” Brown said.

A fully formed adult zebra or quagga mussel has never been detected in Colorado waters. However, the larval stage of the mussels, known as veligers, were detected in 2017 in Green Mountain Reservoir in Summit County, and the reservoir is still considered suspect for quagga mussels.

For detection, biologists perform three types of sampling to target three life stages of mussels. CPW confirms all visual detections with DNA analysis to confirm genus and species. If no additional detections are verified in 2020, Green Mountain Reservoir will be delisted.

In 2019, crews sampled 179 standing and four flowing waters statewide for veligers. In addition to sampling efforts performed by CPW, the National Park Service contributed 38 plankton samples. No zebra or quagga mussels were detected in Colorado.

For more information about CPW’s prevention program, visit