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July 24, 2017

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Zebra mussel’s arrival threatens Lake Mead’s ecosystem

Twenty years ago the tiny zebra mussel was unknown in North America. But somewhere the tenacious invader hitched a ride on a boat from Europe and settled in the Great Lakes.

Within a decade, zebra mussels were fouling the water intakes for nuclear power plants, ruining pleasure boats and wiping out freshwater ecologies throughout the eastern United States and Canada. Federal, state and local agencies worked unsuccessfully to contain the invasion to the Great Lakes, then to the Mississippi River and its tributaries.

Until Friday, the invader hadn't been seen west of the Continental Divide. Now it has been found in Las Vegas' back yard.

The zebra mussel or a close relative - scientists are working on a final identification - has been found in Lake Mead. The discovery has officials from federal, state and local agencies reeling, attempting to ascertain the level of threat to their various operations - and the very future of Lake Mead as a fish habitat.

"This is almost heartbreaking news that the mussels are here," said Kent Turner, resource management chief for the National Park Service's Lake Mead National Recreation Area. The implications of the discovery are huge not just for the lake, but for all the downstream users on the Colorado River because the larva from the mussel can float freely in the water.

Other Western states, too, could face the invasion as the mussel travels with boats from lake to lake.

Any boat that uses Lake Mead - the most popular in the West - could advance the invasion, just as a boat was probably responsible for bringing the animal into Lake Mead.

"All the Western states are highly concerned about this," Turner said. The states, along with regional water system operators including the Southern Nevada Water Authority and federal officials, were scheduled to meet Jan. 31 in Las Vegas to discuss the zebra mussel threat. The discovery three weeks before the meeting of the 100th Meridian Initiative, the unsuccessful cross-agency effort to contain the mussel, brings new urgency to the gathering, he said.

Containment efforts will continue, but now must also include response to areas already infected. "It certainly is going to be very expensive to respond to this," Turner said. "The implications are very large for what it can mean both ecologically and in terms of infrastructure."

The mussel has the potential to profoundly alter the ecology of Lake Mead, which now is a fecund site of fish spawning and waterfowl year round. The mussel works as a filter, straining out the microscopic plankton that form the basis of the entire ecology of the lake.

The U.S. Geological Survey warns that plankton levels in other lakes invaded by the mussel have dropped by more than 90 percent.

Turner warned that the mussel could have other effects, including to Southern Nevada's water system. Las Vegas and its suburbs now take 90 percent of their drinking water from Lake Mead. But the mussel has fouled water systems in lakes that it has colonized in other parts of the country.

Hydroelectric plants, nuclear power plants, public water supply plants and industrial facilities were virtually knocked out by huge colonies of the mollusks before managers learned how to respond to the invader. Although just an inch long, densities as high as 700,000 per square yard have been found at water intakes on the Great Lakes, according to the Geological Survey.

The same agency warns that navigational buoys have been sunk by the weight of the mussels, docks have been destroyed, and the mussel can corrode steel and concrete over time.

Southern Nevada Water Authority spokesman J.C. Davis said his agency's priority is to determine whether the mussel has colonized the two intakes that bring up nearly all of the region's drinking-water supply.

But the Water Authority has some good news for consumers.

The agency had the foresight to install a system that kills the animals on the second intake, or straw, completed four years ago. The system pumps the chemical potassium permanganate into the water around the intake. Davis said such a system could also be installed in the first intake, which was completed in 1971.

Water system managers in the West benefit from having learned from years of damage done by the mussel back East.

"Back East it's been a big issue and has been for years," Davis said. "The remedies are fairly well understood. It doesn't threaten our ability to deliver water. It is just an operational headache we will have to deal with."

Bob Muir, spokesman for the Metropolitan Water District of Southern California, said his board members were informed of the discovery of the zebra mussel in Lake Mead and are concerned about the potential for the animal to foul irrigation and water supply systems.

He said that like the Water Authority, the district has known of the potential for infestations of zebra mussels and has incorporated treatment systems into its infrastructure. Still, the agency is concerned.

"Like many states and agencies, we are assessing what these discoveries will mean," Muir said.

Bob Walsh, a spokesman for the Bureau of Reclamation, which operates Hoover Dam and irrigation structures for millions of acres of farmland in the California and Arizona deserts, said his agency is taking a similar approach.

One of the first steps is to find out whether the mussel has migrated to the dam itself, he said.

The agencies are still trying to ascertain the extent of the invasion because the discovery is still just a few days old. Workers on Saturday repairing a breakwater damaged by high winds a day earlier at the Las Vegas Boat Harbor discovered some of the mussels on a cable within the water.

The workers contacted Wen Baldwin, president of the Lake Mead Boat Owners Association. He has worked as a volunteer to keep the mollusk out of the lake for years.

"These things will get into the boats, they will get into the cooling systems, they will attach and plug them up and burn out the engines," Baldwin said. "It's going to be a maintenance nightmare."

Baldwin has documented successful interdiction of at least three boats destined for Lake Mead with colonies of zebra mussels over the last six years. He identified the mussel over the weekend after the discovery.

"It would have come in on a boat. Exactly where from, at this point we don't know," he said.

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