Media Contacts:
Steve Gonzalez, CDFW Communications, (916) 804-1714
Adeline Yee, California State Parks, Newsroom@parks.ca.gov
Maggie Macias, California Department of Water Resources, media@water.ca.gov

Invasive Non-Native Golden Mussel Discovered in the Sacramento-San Joaquin Delta

Golden mussel (Limnoperna fortunei), an invasive, non-native freshwater bivalve, was recently discovered in the Port of Stockton by California Department of Water Resources staff while conducting routine operations. Suspected golden mussels have also been identified at O’Neill Forebay in Merced County and are currently undergoing genetic testing for confirmation.

This discovery is the first known occurrence of golden mussels in North America. The species poses a significant immediate threat to the ecological health of the Delta and all waters of the state, water conveyance systems, infrastructure and water quality.

In waterways where this species is present, heavy encrustations of golden mussels have blocked municipal and industrial water intakes, necessitated ongoing biofouling removal, harmed native species in the ecosystem, increased water clarity due to intense filter feeding, and diminished water quality.

The California Department of Fish and Wildlife (CDFW), California State Parks, California Department of Water Resources (DWR), U.S. Fish and Wildlife Service, Bureau of Reclamation, and other state, federal, and local agencies regularly coordinate through the Aquatic Invasive Species program. This partnership aims to limit the spread of invasive species in California’s waterways, which cause damage to native species and the ecosystems they need to survive.

Golden mussels were likely introduced to California by a ship traveling from an international port. They are likely to spread throughout the Delta and through the water conveyance systems associated with it. Without containment, golden mussels are likely to spread to other freshwater bodies in California, and to other ports and inland waters of North America, and abroad.

Following the initial discovery of golden mussels in the Port of Stockton, observations of additional mussels have been made on monitoring equipment downstream. Species confirmation is pending for these organisms. Golden mussels are similar in appearance, biology, and impacts to quagga and zebra mussels and are a continued priority for prevention and containment in inland waters of Southern California and across the state.

Golden mussels are native to rivers and creeks of China and Southeast Asia. They are known to be established outside of their native range in Hong Kong, Japan, Taiwan, Brazil, Uruguay, Paraguay and Argentina. The initial introductions to these countries were also likely the result of ships from biofouling on the hulls and/or ballast water release. In most cases, the invaded range has expanded upstream from the point of introduction and inland from ports through local, human-mediated pathways. Within the invaded range significant impacts are widely documented resulting from the dense colonization of golden mussels on hard surfaces.

The California Natural Resources Agency and its partners call upon everyone working and recreating in waters of the state to clean, drain and dry watercraft and equipment every time it is removed from a waterbody. This simple measure has served to prevent spreading quagga and zebra mussels and is equally effective in stopping the overland spread of golden mussels. DWR is now conducting boat inspections at O’Neill Forebay in an effort to reduce the spread of aquatic invasive species.

CDFW is continuing to work with state, local, and federal agencies to enhance monitoring efforts, communicate additional detection and response information, and coordinate on potential next steps. Please report organisms observed in California suspected to be golden mussels to CDFW’s Invasive Species Program. Include the specific location of the observation, and at least one clear close-up photograph of the organism, and your contact information. Submit reports via one of the following options:

Online at https://wildlife.ca.gov/Conservation/Invasives/Report
Via email to invasives@wildlife.ca.gov
Via telephone to (866) 440-9530

To prevent the spread of invasive mussels, be sure to clean, drain and dry your boats. Learn more at California State Parks’ Division of Boating and Waterways webpage: https://dbw.parks.ca.gov/StopQZ.