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Quagga mussels in Arizona: Understanding the enemy

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PHOENIX – As the invasive species coordinator for the Arizona Game and Fish Department, part of Tom McMahon’s job is to stop the destructive quagga mussel from spreading.

The mussels have been wreaking havoc in the Great Lakes regions since the 1980s, and since 2007 or before they’ve been colonizing waterways in Arizona. Here’s McMahon’s take on the threat.

The enemy

The quagga mussels are striped, freshwater mollusks that can live for three to five years. In a single breeding cycle, they can release 30,000 to 40,000 fertilized eggs, or 1 million fertilized eggs in a year.

“In the Great Lakes, they were reproducing two, maybe three times a year,” McMahon said.

With the warmer waters in Arizona, McMahon said that the general thought was the quagga mussel wouldn’t thrive here. However, they began to reproduce five to six times a year, quickly establishing themselves along the Colorado River and hitching a ride on the Central Arizona Project.

Potential damage

There is a looming threat of damage to Arizona waters. As a filter feeder, the quagga mussel suck from water the phytoplankton that serves as the base of the food chain. In large enough numbers, they can disrupt ecosystems.

McMahon said that recreational activities could also be affected. This includes detrimental effects to fishing, something that hasn’t happened yet, as well as fouling propellers and causing other damage to boats.

The main threat, though, is quagga mussels’ ability to block Arizona’s most precious resource if colonies disrupt intakes and other waterworks.

“We move water for electricity, we move water for even salmon runs for Pete’s sake,” McMahon said. “We move water, that’s what we do. These mussels clog that up and that’s not a good thing for us.”

Fighting back

McMahon said that many of the proposed solutions to rid waters of the invasive species aren’t feasible. He said the best way to get rid of the mussels would be to completely empty the lakes and dry them up, which would create an obvious issue with those who use the lakes every day.

To treat the mussels in certain areas where they’ve been blocking pipes, like dams along the Colorado River, McMahon said certain chemicals have been used to kill them.

“There are chemicals that kill them,” McMahon said. “But it kills everything else too.”

He said this process works best in smaller systems, and it’s expensive. To treat an entire lake, it would also take “a ridiculous amount of it.”

And even with the ability to kill mussels, there is no way to get rid of their shells. McMahon said the beaches in the Great Lakes region have been rendered unusable because of the shells that scatter the shorelines, and the sharp pieces often injure people. That has yet to happen in Arizona.

“They are like snowbirds; they kind of love this area,” McMahon said. “Every time we think we’ve found a way to fight back, they always have a twist.”


The strongest method of treatment so far by Game and Fish, McMahon said, is education. Aiming to keep boaters from inadvertently transporting quaggas from infested water, the department advertises the slogans “Clean, drain, dry” and “Don’t move a mussel.”

Cleaning means washing every part of a boat, trailer and equipment of mud, plant and animals.

Drain means eliminating all water from the boat, including livewells, ballast and engine.

Dry means making sure a boat is completely dry before launching someplace else.

“It’s everybody’s problem,” McMahon said. “Unless we go at this as a coordinated effort, it’s going to spread.”