The propeller of a cabin cruiser boat covered by quagga mussels is inspected at Highline Lake State Park. An inspection can take as little as 10 minutes if a boat is clean and dry, but if it has to be decontaminated, it can take anywhere from an hour to a couple of days, depending on the level of contamination.

Heading into another boating season, Colorado’s waters remain free of invasive and damaging mussels but Colorado Parks and Wildlife officials are worried about the growing number of heavily infested boats entering the state.

Eighty-six vessels fully infested with zebra or quagga mussels were intercepted through Colorado’s watercraft inspection program last year, up from 51 the previous year and just 16 in 2017, the agency said this week. A total of 281 boats were found with mussels attached, but many of those cases involved boats that had just a few mussels that could be easily removed by inspectors.

The number of boats requiring decontamination under the program grew from 19,111 in 2018 to 22,947 last year.

CPW says 481,543 boats were inspected last year, 7,000 more than the previous year. The agency authorized 72 locations to perform inspections and decontaminations last year.

Invasive mussels are found in waters in several nearby states, including Utah, Arizona, Kansas, Oklahoma and Texas. They can multiply and clog water delivery pipes, cover docks and shorelines and ruin powerboat engines, among other damaging impacts.

CPW says no fully formed, adult zebra or quagga mussels ever have been detected in Colorado waters, but larval mussels known as veligers were detected as recently as 2017 in Green Mountain Reservoir in Summit County, and the reservoir is still considered suspect for quagga mussels. Biologists do sampling targeting the various life stages of mussels and DNA analysis is used to confirm the presence of quagga or zebra mussels. If no additional detections are verified this year Green Mountain Reservoir will be considered free of invasive mussels.

Last year, crews sampled 179 standing waters in the state for veligers, and four flowing waters, and the National Park Service also contributed 38 plankton samples for testing. No indications of invasive mussels were found.

Blue Mesa Reservoir is among those water bodies near the top of the list statewide for inspections last year. More than 18,000 inspections occurred at Blue Mesa last year, resulting in 625 decontamination procedures. Pueblo Reservoir had the most inspections — 73,435 — and 2,275 decontamination procedures occurred there.

CPW spokesman Joe Lewandowski said decontamination targets plants and other species besides just mussels, and inspectors will err on the side of caution in taking measures such as spraying down boats. Other measures can include running hot water through engines and flushing out ballast tanks and anything else that holds water.

Lewandowski said fully infested boats have to undergo more involved decontamination, and sometimes have to be set aside for several days and dried out. Heavily infested boats can have mussels in places such as inside the pontoons on pontoon boats, he said.

A breakdown of water bodies where mussels detections occurred last year wasn’t immediately available from CPW.

A major concern in western Colorado especially is boats coming to the state from Lake Powell, which is heavily infested.

“You go to Lake Powell for a week and you’re going to pick up stuff. It’s almost impossible not to,” Lewandowski said.

Lake Powell lacks strong measures to ensure decontamination of boats leaving that reservoir. Lewandowski said boaters coming back from Powell are asked to call CPW for a pre-inspection before taking their boat to Colorado waters.

“We’ll spray it off if necessary,” he said.

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