A cutaway shows a 2-inch pipe clogged with zebra mussels. Quagga mussels, known by some as the zebra's "nasty cousin," have turned up at Lake Mead and might have spread into California. Don Schloesser/Great Lakes Science Center, National Biological Services Click image for enlargement. Graphic by Mike Johnson.

Divers have collected what appear to be invasive mussels in Lake Havasu and in a nearby California reservoir that holds water for delivery to Los Angeles, adding to fears that nuisance zebra-type mollusks found in Lake Mead this month have spread, biologists and Southern Nevada water officials said Thursday.

The mussels were discovered Wednesday morning on buoy cables and concrete 30 feet to 50 feet below the surface of Lake Havasu near the Whitsitt intake facility for the Metropolitan Water District of Southern California.

The find expands the problem that water and wildlife agencies face to prevent colonies of mussels from clogging pipelines and impacting native species.

Biologists were trying to identify the mussels positively late Thursday, but some of the scientists close to the issue said the creatures appeared to be non-native quagga mussels like those found Jan. 6 in Lake Mead. They don't have the appearance of freshwater mussels native to North America.

If Wednesday's find is confirmed, it would mark the first reported case of zebra or quagga mussels in California, said Bob Muir, spokesman for the Metropolitan Water District.

California's largest water agency is now checking the rest of the Colorado River Aqueduct and its related facilities for signs of infestation, Muir said.

Jon Sjoberg, supervising biologist of the Nevada Department of Wildlife, formed a circle the size of a silver dollar with his thumb and index finger and compared the invasive mussel problem to "trying to contain a hornets' nest by dropping a laundry basket over it with holes that big."

It was inevitable, he said, that non-native mussels eventually would show up in other parts of the Lower Colorado River system after they were found two weeks ago near marinas in Lake Mead's Boulder Basin and later at the state fish hatchery on Lake Mead.

"I was a little surprised that what appears to be quagga mussels showed up that soon farther down in the system," Sjoberg said during a break of the California-Nevada Amphibian Populations Task Force. The task force was meeting at the University of Nevada, Las Vegas to discuss native frog issues.

National Park Service staff members and federal biologists have checked for invasive mussels in Lake Mohave downstream of Hoover Dam but have not reported finding any. The mussels can survive in a few inches of water in a boat's live well, bilge or water from an engine's cooling system. On some weekends as many as 5,000 boats are launched at Lake Mead National Recreation Area, a Park Service spokeswoman said.

Sjoberg said it's unclear whether quagga mussels were introduced first in Lake Mead by a boat hauled to the lake from the Great Lakes region or whether Lake Mead's infestation came after a boat or piece of equipment had been put in Lake Havasu from infested waters outside Nevada.

"It could have worked in reverse. We just don't know," he said.

His comments came at about the same time a local water official informed the Southern Nevada Water Authority board that invasive mussels had been found in Lake Havasu.

The announcement was made by Southern Nevada Water System Director Ron Zegers, who oversees the massive network of pipelines, pumps and plants that draws untreated Colorado River water out of Lake Mead, treats it and distributes it throughout the Las Vegas Valley.

Zegers said access to the Colorado River Aqueduct "provides the mussel with a whole avenue of spread into California."

The aqueduct delivers water to much of urban Southern California, including Los Angeles and San Diego.

Zegers and other officials in Southern Nevada still are assessing the extent of the infestation at Lake Mead, but so far the mussels are not viewed as much of a threat to municipal water and sewer infrastructure at the reservoir.

A dive team hired by the water authority is scheduled on Saturday to search for mussels on and around the agency's two water intakes at Lake Mead.

Zegers said one of the intakes is equipped with a chemical feed designed to repel mussels; the other is not. "We'll probably have to look at some temporary system and a permanent chemical feed system on Intake One," he said.

Water authority spokesman J.C. Davis said a chemical feed system is already in the plans for the valley's third water intake, which is now in development and expected to go online in 2012.

A new sewage out-fall system that one day will inject treated wastewater into the middle of Lake Mead is also being designed to be mussel proof, said Douglas Karafa, program administrator for the Clean Water Coalition.

Karafa announced Tuesday that the coalition would consult with a mussel expert from the Great Lakes region as it develops its sewage out-fall, which eventually will replace the Las Vegas Wash as the primary conduit for the valley's treated waste to reach Lake Mead.

Quagga mussels are from the same genus as the more commonly known zebra mussel species but are slightly bigger and have been described by some in wildlife circles as zebra mussels on steroids.

Karafa called the quagga "zebra's nasty cousin."

Zegers said, "They're just bigger, and they're worse."

Until quagga mussels were found this month in Lake Mead, they had not been found previously in the United States west of the Great Lakes region or a stretch of the Mississippi River between St. Louis and Alton, Ill.

Like zebra mussels, quagga mussels are freshwater mollusks that can multiply rapidly, with a single female laying as many as 1 million eggs.

Both species were introduced accidentally to the Great Lakes region in the ballast water of ships from eastern Europe and the Ukraine.

These non-native mussels have caused billions of dollars in damage and preventive maintenance costs in the Great Lakes region and elsewhere in the Midwest and eastern United States by clogging water supply pipelines, power plant cooling systems and marine equipment. They were found in Lake St. Clair near Detroit in 1988 after being transported to the region in the ballast of a ship.

Zegers said colonies in the Great Lakes have been known to reach densities of 700,000 mussels per square meter.

The mollusks can completely plug pipes up to 12 inches in diameter, and can restrict flow in larger pipes. Their colonies also can speed up the corrosion of pipes and other underwater infrastructure, Zegers said.