Geo Hirst of Sin City Scuba Diving Charters surfaces after checking several water intake pipes for quagga mussels at Lake Mead Saturday. The Southern Nevada Water Authority’s intake pipes were relatively free of the mollusk, which has been confirmed in Lake Mohave downstream of Hoover Dam. Photo by Ronda Churchill

For a bivalve mollusk no bigger than a silver dollar, this quagga character really gets around.

Less than a week after the invasive mussel was confirmed in California for the first time, the National Park Service has discovered quagga in Lake Mohave, about 60 miles downstream from Hoover Dam.

Park Service divers on Saturday found the live, zebra-type mussels on docks and the hulls of houseboats at Katherine Landing, just north of Davis Dam. They were positively identified as quagga by a U.S. Fish and Wildlife Service scientist on Sunday.

The scientist also inspected mollusks collected from a depth of about 110-feet of water at the Kingman Wash area of Lake Mead and confirmed them to be quagga mussels.

Samples taken last week from Lake Mead's Callville Bay Marina came back quagga as well.

Until Jan. 6, when they turned up in Lake Mead's Boulder Basin, quagga mussels had never been found west of the Mississippi River. They now have been confirmed in eight separate locations spanning some 160 miles of the Colorado River.

"We do not know the point of infestation, and we may never know," said Julian Rhinehart, spokesman for Lake Mead National Recreation Area. "That's probably going to remain a mystery."

Though they pose no health risk to humans, the quagga and its cousin, the zebra mussel, can crowd out native species and clog water supply pipelines, power plant cooling systems and marine equipment.

The mussels have caused billions of dollars in damage and maintenance costs in the Great Lakes region, where they were introduced accidentally by ships from eastern Europe and Ukraine.

So far, though, the infestation at Lake Mead appears relatively minor. There have been "no signs whatsoever" of quagga at Hoover Dam, said Bob Walsh, spokesman for the U.S. Bureau of Reclamation.

He said crews will spend part of this week checking for mussels on some submerged concrete surfaces, but at this point it is unclear whether quagga is even worth worrying about at the dam.

"I seriously doubt whether they would disrupt water deliveries or power generation. Those are big, huge systems," Walsh said. "I think it's very unlikely that they (the mussels) could cause any problems."

During an inspection dive at Lake Mead on Saturday, about 50 scattered quagga mussels were found on one of the Southern Nevada Water Authority's intake pipes down to a depth of about 90 feet.

No mussels were found inside the pipe, or anywhere on the authority's second intake, spokesman Scott Huntley said.

During the same dive, quagga mussels were found on stainless steel screens that cover the mouth of Basic Water Company's intake pipe at Lake Mead, but not enough to disrupt the flow of water.

"Our system is flowing fine, so whatever is there, it's not bad. It's not impeding operations at all," said Mark Paris, president and CEO of Basic Water Co.

Basic's intake supplies water to the city of Henderson, Lake Las Vegas, the chemical plants along Lake Mead Parkway, and the Nevada trout hatchery at Lake Mead.

Trout releases from the hatchery have been suspended after mussels were found throughout the facility.

Henderson Utility Services Director Dennis Porter said no quagga have been found at the city's water treatment plant downtown, but "we're still looking."

Though mussels could cause some problems at the plant, local water users need not worry about finding quaggas in the pipes and toilet tanks at their homes, Porter said. "There's no way they can live in the distribution system."

Huntley said the Southern Nevada Water Authority plans to recheck its Lake Mead intakes at least once every three months from now on. Paris said Basic Water Co. would do the same.

"It could be that we'll have to replace the screens every three or four months" because of the mussels, he said. "Everybody is just learning about this."