History and Background

Quagga and zebra mussels arrived in the United States from Europe in the 1980s and spread to many eastern waterways, rivers, and lakes. Quagga mussels were discovered in Lake Mead, Lake Mojave, and Lake Havasu on the Colorado River in January 2007, and zebra mussels were confirmed to be present in San Justo Reservoir in California in January 2008. Quagga mussels were later confirmed in Lake Powell in 2013. Invasive mussels have since spread to reservoirs in southern Arizona and California.

The primary way mussels are spread from one water body to another is on recreational boats that are used in infested water and then transported to another water body. The mussel larvae (veligers) are microscopic and can survive in small amounts of water left on the boat and the juvenile and adult mussels can attach themselves to the boat and survive transport. Veligers can also be moved within connected waters by natural currents. Not all mussel introductions will lead to an infestation, as mussels require certain conditions and water quality to survive and reproduce. Mussels are almost impossible to eradicate if they are able to survive, reproduce and infest a water body.

Impact of Mussels

Invasive mussels pose significant challenges for Reclamation because they are prolific breeders that permanently settle on or within water facility infrastructure. Maintaining and operating water supply and delivery facilities, water recreation, and other water-dependent industries in mussel-infested water bodies is significantly more complex and expensive. Mussels also affect public recreation, the natural ecology, and water quality. Shell fragments degrade swim beaches, watercraft inspection and decontamination requirements increase time and cost for boaters, and populations of game fish can be affected. A single adult dreissenid mussel can filter approximately a liter of water each day, detrimentally reducing the availability of algae and zooplankton for native and endangered mollusks and other aquatic organisms, including fish. Extensive filtration has also increased water clarity, leading to the proliferation of aquatic weeds that can further augment the ecosystem.

Reclamation’s Response

Reclamation utilizes a variety of strategies to help reduce the spread and impacts caused by mussels to Reclamation facilities and structures- specifically: the prevention of mussel spread- through partnerships for watercraft inspection and decontamination; early detection and monitoring; facility vulnerability assessments; research on mussels control and novel monitoring technologies and; public outreach and education.

Reclamation created an invasive mussel corporate task force to coordinate a Reclamation-wide approach to managing quagga and zebra mussels. By developing a corporate strategy, Reclamation integrates the various strategies to meet its needs and facilitates communication and dialogue within Reclamation. Additionally, Reclamation established a mussel monitoring and detection program in 2009 headed by the Ecological Research Laboratory (Eco Lab) at the Technical Service Center. The goal of this program is to detect the first stages of mussel exposure at Reclamation reservoirs, and to develop protective measures to prevent mussel spread and mitigate the effects of a future infestation.

More Information

Fact Sheets

Related Websites

Zebra and Quagga Mussel Sightings Distribution Map

Last Updated: 8/21/20