updated 8/20/2007 3:37:43 PM ET 2007-08-20T19:37:43

An invasive mussel that made its way west of the Rocky Mountains seven months ago is spreading rapidly, just the scenario most feared by officials running water systems supplying millions of people across the Southwest.

The thumb-sized quagga mussels, which can clog pipes and gum up waterworks, have already been discovered in lakes Mead, Havasu and Mojave on the Colorado River and in two major aqueducts that supply water to Southern California and Arizona.

Officials announced this month that they had also found tiny quagga larvae in Lake Powell on the Arizona-Utah border, although no adults have yet been found. Most interior lakes have staved off infestations — for the time being.

Quagga mussels, close cousins of the better known zebra mussels, are almost impossible to totally exterminate. The small clam-like creatures damage local aquatic life and can cause millions of dollars in damage to water facilities. They also damage marinas and boat motors.

The big fear is that the mussels will infiltrate canals and pipelines feeding the Southwest's vast system of reservoirs and water treatment plants, sending maintenance costs skyrocketing.

800 found in Colorado River Aqueduct
And, already, the mollusks are making water treatment managers squirm.

In March about 800 mussels were found in the 242-mile Colorado River Aqueduct, which supplies water to 18 million people, said Bob Muir, a spokesman with the Metropolitan Water District of Southern California.

Portions of it were closed for 10 days in July to inspect the system and destroy larvae.

Officials are spending $5 million for a special control system that includes increased water chlorination and equipment that will help them evaluate quagga infestations, Muir said.

Alien invaders"It's a matter of controlling and containing them. We'll never be able to truly eradicate quaggas from our system," he said. "We've seen in the Great Lakes that when they mass produce, they can clog pipelines, they can disrupt water distribution systems."

A few mussels have also been discovered in the Central Arizona Project aqueduct, which draws water from Lake Havasu and delivers it as far south as Tucson.

The quasi-public agency is trying to prevent their spread by stocking the aqueduct with redear sunfish, which are thought to eat the mussels, said John Newman, an assistant general manager.

"We just really don't know what will happen at this point," Newman said.

Other agencies are quickly creating plans to deal with their spread.

Scrape strategy
The Salt River Project, which provides water and power to the Phoenix metropolitan area, plans to scrape them away, use pesticides and try special paint coatings that repel the mussels. Though none have been spotted in the project's reservoirs, their spread is practically inevitable, said Brian Moorhead, an environmental scientist for the public agency.

Prevailing wisdom is that ships emptying ballast water are responsible for introducing quagga mussels to the Great Lakes in the 1980s, where they've caused at least $1 billion in damage. To come out West, they likely hitched rides inside ballast tanks or on the bottom of boats that weren't washed carefully.

In 2006, authorities exterminated zebra mussels at a quarry in Virginia by raising potassium levels to poison them. But that would be logistically difficult in larger bodies of water and could harm plants or animals, said University of Texas at Arlington biology professor Robert F. McMahon, who studies zebra and quagga mussels.

Once quagga mussels arrive, they're usually there to stay, he said.

"The best way to avoid these problems is to prevent them in the first place," McMahon said. "There are all sorts of non-indigenous species that have been introduced to the United States. This is just an example of what some of these species can do."

In an attempt to prevent the mussels' spread, authorities are urging boat owners to thoroughly inspect and wash their vessels before putting them in the water. At some lakes, including Lake Powell, boats must be decontaminated before entering the water.

Copyright 2007 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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