"Reactive approach means you're going to live with the mussels. You're going to control them, but you're going to live with them," he said in a presentation last week to the Lake Mead Water Quality Forum.

He projected that as the infestation sets in and begins to clog hydroelectric power cooling pipes and other hardware in Hoover Dam's operations, the maintenance-and-control bill could reach $1 million a year, especially if pipes get plugged with quagga colonies.

That would cause turbines to overheat and shut down until cooling pipes can be reamed of the pesky mollusks.

"This is an evil critter, not good," Willett said after Tuesday's meeting at the Southern Nevada Water Authority's River Mountains Water Treatment Plant in Henderson.

"It is going to cause a lot of problems when we're going to have to install control measures," he said.

Among the options for controlling the invasion is to use a bacteria product that targets the quagga mussels.

While that method is still being developed, Willett said, "It looks very promising."

Other choices are mechanical filters and using chemicals like chlorine to kill them, or a combination of filters and ultraviolet light.

At the end of the day, though, there would be shells from dead quaggas to dispose of and discharge permits to obtain.

So far, conditions for quaggas to thrive appear to be more than adequate at Davis Dam at the south end of Lake Mohave, north of Laughlin.

In October, a colony coated the dam's exterior penstock gate like carpeting.

A month later, downstream at Parker Dam on Lake Havasu, quaggas covered sampling plates used to monitor them in the fore bay.

"At Parker Dam, there is a lot of colonization. At Parker, there is no hope. They colonize repeatedly," Willett said.

With warmer year-round temperatures than bodies of water in the Great Lakes, quaggas are able to reproduce six times a year instead of two.

In addition, Havasu has the right mix of food, calcium and dissolved oxygen to sustain colonization.

With that, Willett said, "You're going to get mussels. I'm not surprised."

Near Hoover Dam, quaggas have been found more than 200 feet deep in Lake Mead.

Not only do they pose a threat to the cooling pipe system for hydroelectric turbines, but also to the network that supplies domestic water for workers and visitors at the dam.

They prefer to cling to flat, stainless steel structures where water flows less than 6 feet per second.

"Mussels really like stainless steel. They don't like copper or brass," Willett said.

A cousin of the quagga, zebra mussels, has turned up in Colorado's Lake Pueblo State Park and in California's San Justo Reservoir in San Benito County, off the California Aqueduct system.

According to the 100th Meridian Initiative, an organization that tracks the spread of aquatic nuisance species, quagga mussels are native to Ukraine's Dneiper River drainage.

Like the zebra mussel, they were transported to the Great Lakes in the ballast water of ships in the mid-1980s.

Quagga mussels were discovered Jan. 6, 2007, in Lake Mead's Boulder Basin.

Biologists believe they hitchhiked on a boat that was launched in the lake.

In a statement posted Jan. 16 on the California Department of Fish and Game's Web site, Resources Secretary Mike Chrisman said:

"The discovery of zebra mussels in a central California waterway has us very concerned. Like its relative the quagga mussel, this species can cause significant environmental, recreational and economic impacts once established in a body of water. It is important that boaters do everything they can to help stop their spread."

Jon Sjoberg, supervising fisheries biologist for the Nevada Department of Wildlife in Las Vegas, said his colleagues in California are puzzled how zebra mussels, instead of quaggas, arrived in central California first after existing previously in the Great Lakes and Midwest regions.

The source is unknown, he said, although there's speculation that anglers or bait buckets could have transported them, even ducks or waterfowl.

"It's like they dropped out of the sky," Sjoberg said.

Contact reporter Keith Rogers at krogers @reviewjournal.com or (702) 383-0308.