Click the LHM Logo above to return to our main page.

Important Information on protecting our lake.

Invasive mussels found at CAP intakes on Lake Havasu


Officials fear the invasion could spread to the interior of Arizona

PHOENIX -- Divers have found quagga mussels at the Central Arizona Project (CAP) intakes at Lake Havasu, and officials fear this invasive mollusk could spread into central Arizona lakes.

The CAP canal is one pathway for these mussels to spread into central Arizona, but these aquatic invaders could also hitchhike on boats coming from the Colorado River lakes that have already been infested.

“Quagga mussels could spread into Lake Pleasant, if they haven’t already. These prolific invaders pose a significant, multimillion-dollar threat to our lakes, rivers, streams and water systems,” says Larry Riley, the fisheries chief for the Arizona Game and Fish Department.

The CAP canal provides water to the interior of Arizona and stretches into the Phoenix and Tucson areas. Lake Pleasant on the northern edge of Phoenix is filled each year with Central Arizona Project water.

Efforts are underway to examine this long canal stretching across the state to determine if these mussels have established themselves.

Bob Barrett, a spokesperson for the Central Arizona Project, emphasized that quagga mussels do not pose a threat to the public health or to the water supply. “We’ll do whatever it takes to keep the water flowing. If they begin to build up, we’ll scrape them off.”

During the last two weeks since their discovery at Lake Mead on Jan. 6, quagga mussels have been confirmed at lakes Mohave and Havasu, including adjacent to the structure that pumps water from Havasu to parts of southern California. The invasive mussels have also been found at a fish hatchery in Nevada that provides trout to Lake Mead and Lake Mohave. Fish deliveries from that hatchery have been suspended until new procedures are in place to avoid the spread of these mussels. Efforts are continuing to determine the extent of the spread so far.

The Dreissena species of mussels, which includes two closely related mussels, the zebra and quagga, are less than an inch long, but are extremely prolific. A single one of these mollusks is capable of producing up to a million microscopic larvae in a year.

Quagga mussels can be found at much lower depths than zebra mussels, which is not good news for the deep reservoirs often found in the West. These rapidly-spreading invaders can clog pipelines; damage machinery, such as boat engines; harm fishery resources and befoul bodies of water with waste. In time, they can permanently alter a lake’s ecosystem.

The Arizona Game and Fish Department, National Park Service, California Department of Fish and Game, and the Nevada Division of Wildlife are urging boaters and other water recreationists to take positive action to avoid spreading this aquatic invasive species. Boaters (including personal watercraft, canoe and kayak users), divers and anglers should take the following precautions:

  • Drain the water from your boat motor, livewell and bilge on land before leaving the lake.         

  • Flush the motor and bilges with hot, soapy water or a 5-percent solution of household bleach.

  • Inspect your vessel and trailer, removing any visible mussels, but also feel for any rough or gritty spots on the hull. These may be young mussels that can be hard to see.

  • Wash the hull, equipment, bilge and any other exposed surface with hot, soapy water or use a 5-percent solution of household bleach.

  • Clean and wash your trailer, truck or any other equipment that comes in contact with lake water. Mussels can live in small pockets anywhere water collects.

  • Air-dry the boat and other equipment for at least five days before launching in any other waterway.

  • Remove any mud or vegetation from your boat or trailer – mussels can hide and hitchhike in this material.

  • Do not reuse bait once it has been in the water.

  • Clean sensitive gear (diving and fishing gear) with hot water (140 degrees F) or a soak in warm saltwater (1/2 cup of iodized salt per gallon of water) and air-dry before use elsewhere.

These small invasive mussels, which originally came from Eastern Europe, have been causing multimillion-dollar problems in the Great Lakes and the Mississippi River Basin. The Colorado River is 1,000 miles farther west than any previously known colonies of these mollusk invaders.

For additional information on this aquatic invader and others, visit the Arizona Game and Fish Department Web site at azgfd.gov, protectyourwaters.net, 100thMeridian.org, and the U.S. Geological Survey Web site.

Frequently Asked Questions

What are quagga or zebra mussels?

Zebra mussels (Dreissena polymorpha) are small, freshwater bi-valve mollusks (relatives to clams and oysters) that are triangular in shape with an obvious ridge between the side and bottom. The zebra mussel gets its name from the black- (or dark brown) and white-striped markings that appear on its shell.


Where did quagga or zebra mussels come from?

Quagga mussels are native to the Dneiper River drainage of the Ukraine. Zebra mussels are native to the Caspian, Black, and Azov seas of Eastern Europe. These exotic mussels were first discovered in the United States in Lake Saint Clair, Michigan, in 1988 and are believed to have been introduced in 1986 through ballast water discharge from ocean-going ships. Since their initial discovery, zebra mussels have spread rapidly throughout the Great Lakes and Mississippi River Basin states and other watersheds throughout the eastern and central United States. Quagga mussels have not spread as extensively.

How did these invasive mussels get to Lake Mead?

These invasive mussels in Lake Mead are 1,000 miles farther west than any other known colony of zebra mussels.  The primary method of overland dispersal of these mussels is through human-related activities. Given their ability to attach to hard surfaces and survive out of water, many infestations have occurred by adult mussels hitching rides on watercraft. The microscopic larvae also can be transported in bilges, ballast water, live wells, or any other equipment that holds water. 

What do they eat?

They are primarily algae feeders.  They feed by filtering up to a liter of water per day through a siphon.

Why should we be concerned about these mussels?

These mussels are filter feeders that consume large portions of the microscopic plants and animals that form the base of the food web. The removal of significant amounts of phytoplankton from the water can cause a shift in native species and a disruption of the ecological balance of the lake.

These mussels often settle in massive colonies that can block water intake and affect municipal water supply and agricultural irrigation and power plant operation.  In the United States, Congressional researchers estimated that zebra mussels alone cost the power industry $3.1 billion in the 1993-1999 period, with their impact on industries, businesses, and communities more than $5 billion.

Mussels were only found in one area of Lake Mead. How can that become a problem?

These invasive mussels can live for three to five years and can release 30,000 to 40,000 fertilized eggs in a breeding cycle and one million fertilized eggs in a year.

Do these mussels have any predators?

These mussels do not have many natural predators in North America, but it has been documented that several species of fish and diving ducks have been known to eat them.

What can I do to help?

It is up to each of us to take extra precautions to stop the spread of mussels or any other invasive species. The following actions should be taken with any equipment used in potentially infested waters:

  • All equipment (e.g., dive gear, boats, trailers, motors, etc.) should be visually and tactically (by feel) inspected for the presence of zebra mussels prior to and after use in any water body. Additionally, any vegetation attached to this equipment must be removed and left at the site of origin.

  • Remove all sediment and gritty organic materials; these could actually be zebra mussel veligers (juveniles).

  • Clean and scrub boat hulls, motors, anchors and trailers. Then hose equipment with hot (140° F) and/or high-pressure water.  Bilges, live wells, and any other compartments that could hold water should be drained at the site of origin, and, if possible, flushed with disinfectant or hot water. All boat equipment should be allowed to remain completely dry for at least 24 hours before being used again.

  • Thoroughly clean all equipment in a saltwater bath (1/2 cup per gallon) or with warm tap water (104 ° F). Ensure that all equipment remains completely dry for at least 24 hours before being used again. Pay special attention to those areas and equipment that can hold water.

  • Take similar precautions with waders, bait buckets, and other equipment that can hold water or comes into contact with water.