Dec 15 2014Share

Quaggas Muscle Their Way Into Your City’s Water Delivery System

By Kathleen Ferris

A mussel about the size of a dime is breeding by the millions in reservoirs fed by the Colorado River. These invasive creatures, which can grow a little larger than a quarter, threaten the delivery of water to the Greater Phoenix Metropolitan area. They also can cost you and your cities a lot more than small change.

Quaggas, like most transplants, love Arizona’s weather. Back East these mussels reproduce once or twice a year. In our sunshine and warm water the mussels reproduce up to 10 times a year. These are the types of transplants we don’t want to encourage.

Adult quagga mussels spread by hitching rides on boats, other watercraft and anything that might hold water. Their microscopic larvae can be transported in just droplets of water.

Quagga mussels, natives of Eastern Europe, were first discovered in the U.S. in 1989 in the Great Lakes. In 2007, biologists discovered quagga mussels in Lake Mead, a Colorado River reservoir created by Hoover Dam. Soon, the mussels made their way throughout the Arizona's  Colorado River reservoirs. The mussels have few natural predators in this country and no one has yet found a way to stop an infestation once it begins.

Quagga mussels grow in massive colonies. The mussels live for three to five years and females release up to a million larvae each year. Quagga larvae that survive grow a shell heavy enough to start sinking after about 21 days. The mussels also grow sticky hair-like threads and attach themselves to mostly hard surfaces. Those surfaces include pipes, canals, pumps and grates needed to transport and clean the Valley’s drinking water. Clearing the quaggas out of equipment takes time and money.

The Central Arizona Project operates one of the state’s water-delivery systems. The system includes hundreds of miles of aqueducts, pipes and 14 pumping stations that bring Colorado River water to La Paz, Maricopa, Pinal counties and down to Tucson in Pima County.

The mussels have made their way into some cities’ water systems, including Cave Creek and Scottsdale. Most of the mussels have to be removed manually, shell and all. If you just kill the mussels, their shells fall into equipment and continue to cause problems.

In 2013, Scottsdale found quagga mussels in a pumping station where Central Arizona Project water flows into its system. Employees scrape off some mussels by hand, but most are removed with a high-pressure sprayer and then vacuumed into a container. So far, Scottsdale has been able to minimize damage done to its pumping equipment.

Photo: CAP

Photo: CAP

Salt River Project also delivers water to the Valley. It operates the dams and reservoirs along the Salt and Verde rivers. So far, these lakes in the eastern part of Arizona are quagga free. Each month, SRP biologists send out water samples to be analyzed for quagga larvae. The biologists also use 6-inch by 6-inch plates at different depths in the lakes to monitor for adult mussels. (By the way, SRP also uses these plates in the Phoenix area canal system, but it keeps losing them to well-meaning residents trying to keep the canals clean.) So far, SRP has found a limited number of adult quaggas in the canals.

Researchers are still trying to determine why quaggas are prolific in the Colorado River area but have yet to reach the Salt and Verde rivers on the eastern side of the state.

In addition to damage caused to water delivery systems, quagga mussels harm the environment. For example, quagga mussels are very effective filter feeders and can remove enormous amounts of critical food from the water. This food is needed by other species, especially juvenile fish, to maintain adequate population sizes.

Arizona Game and Fish Department promotes a Don’t Move A Mussel campaign and requires boaters and anglers to clean, drain, and dry their boats and fishing gear. The agency also requires day-use boater to wait five days before moving a boat from an infested lake into another body of water. There is more information about preventing the spread of quagga mussels and a list of infested lakes at Arizona Game and Fish.

For 45 years, Arizona Municipal Water Users Association has worked to protect our member cities’ ability to provide assured, safe and sustainable water supplies to their communities. For more water information visit

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