Two out of five water samples transported for testing in Denver showed evidence of larvae. It's not known if any of the larvae were quagga mussels, which have been found to be more hearty and adaptable, once established, than their zebra cousin.

Glen Canyon National Recreation superintendent Kitty Roberts said in a statement that more samples from the lake are being collected to see if mussels might be present in other areas.

About 300 miles away, full-grown mussels were found in Lake Mead near Las Vegas. It's believed the zebras hitchhiked there on a craft that had in previous days been in the Great Lakes area. Quagga and zebra mussels are also common in the Mississippi River Basin and in watersheds across the central and eastern parts of the country.

Dalton said he believes that the larvae found in Lake Powell came from Lake Mead, which he said has established colonies of the quagga mussel. Dalton said a boater coming from Lake Mead likely didn't know that at least one mussel had attached itself to that person's boat. A single mussel can produce between 100,000 and one million eggs, which need to be fertilized to become larvae.

A new initiative in Utah is placing around 40 personnel around Lake Powell to intercept boaters coming from Lake Mead and other infested areas and make sure they know about the mussel problem and how to properly address it, Dalton added.

Last May and June, decontamination stations were installed at boat launches around Lake Powell. Boaters, in particular those who have recently been in affected areas, are told to wash their crafts with scalding-hot water at those stations before entering the lake.

If adult zebra and quagga mussels are found in the lake, their only known predators are certain fish species and diving ducks. But natural predation is not considered a cure for preventing the presence of mussels or significantly reducing their population.

Dalton said officials in Virginia spent about $365,000 to treat a 12-acre pond used by boaters where mussels were established. A mixture of 50 parts per million of potassium chloride (like the salt used in water softeners) killed off the mussels — a method Dalton said likely wouldn't work here.

"You can imagine trying to treat Lake Powell," he said. Dalton added that if adult mussels do show up, the effort will be to contain or control their presence.

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E-mail: sspeckman@desnews.com