Invasive Mussels Detected in California Waters for the First Time in North America

The golden mussel (Limnoperna fortunei), an invasive freshwater species from Asia, has been detected in California’s Port of Stockton—its first known appearance in North America.

Golden mussels were likely introduced by an international ship, according to the California Department of Water Resources (DWR), which discovered them during routine monitoring. Suspected golden mussels have also been found at O’Neill Forebay in Merced County and are currently undergoing genetic testing for confirmation.

This discovery poses a serious threat to California’s Delta, water conveyance systems, and overall water quality. Golden mussels rapidly colonize hard surfaces, clogging municipal and industrial water intakes and degrading infrastructure. They increase water clarity by intense filter-feeding, which disrupts the ecosystem and threatens native species by altering food webs and diminishing water quality.

The California Natural Resources Agency, alongside agencies such as the California Department of Fish and Wildlife (CDFW) and U.S. Fish and Wildlife Service, has heightened efforts to contain and monitor this invasive species. Agencies are urging anyone working or recreating in state waters to clean, drain, and dry watercraft and equipment to prevent the mussels from spreading.

DWR has implemented boat inspections at O’Neill Forebay to reduce the spread, and monitoring equipment downstream from the Port of Stockton has shown additional mussels, pending species confirmation. Similar in appearance and impact to quagga and zebra mussels, golden mussels have already devastated ecosystems in Asia and South America.

Anyone observing suspected golden mussels in California is encouraged to report them to CDFW’s Invasive Species Program with detailed location information and a close-up photo. Reports can be submitted online, by email at invasives@wildlife.ca.gov, or by calling (866) 440-9530. Learn more about prevention at California State Parks’ Division of Boating and Waterways.