But officials at Lake Powell aren't sure yet whether the quagga mussels have become established there.
Lake Powell has been free of the mussels that have clogged other Colorado River reservoirs and ravaged the Great Lakes region.
The National Park Service said Thursday that samples taken near Glen Canyon Dam and Antelope Point show the presence of mussel larvae and DNA.
Glen Canyon Recreation Area Superintendent Todd Brindle says it's possible the larvae could have washed off boats that had been in mussel-infested waters.
He says divers and remote-controlled vessels will be searching for adult mussels that would signal the startup of a population.
Boat inspections are mandatory at Lake Powell.
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