By Vicky Boyd, Ag Alert
Since the non-native golden mussel was first discovered in October 2024 in the Sacramento-San Joaquin Delta, the potentially pipe-clogging mollusk has spread as far south as Riverside County.
Invasive pest management experts acknowledge eradication is likely impossible. They say the goal now should be to protect noninfested water bodies from mussel introductions. But it won’t be easy.
“Preventing spread to areas that receive delta water via the California Aqueduct is a large challenge,” said Tanya Veldhuizen, program lead for the State Water Project Aquatic Nuisance Species Program. “Currently available technology to prevent the transfer of mussels is very limited and applicable to only very small volumes of water.”
Already, the golden mussel has disrupted maintenance activities at the Port of Stockton and a handful of water providers, and its impact is only expected to grow.
Andrew Genasci, San Joaquin Farm Bureau executive director and a member of the San Joaquin County Golden Mussel Ad Hoc Committee, said the new invader could affect farmers and districts that pump from the delta and flood-control projects. Although flood control may be needed only a few times a year, having a workable system is crucial during heavy rainfall.
“If the pipe is completely encrusted, all of a sudden you can’t pump out the flood waters,” he said.
Delta farmers also may receive a rude surprise as they crank up their irrigation systems at the beginning of the season, only to find pipes are clogged with mussels, he said.
The San Joaquin County Board of Supervisors established the local golden mussel committee to aide communication between state agencies and potentially affected groups in the county.
If history repeats itself, golden mussels could easily spread overland through human-related activities such as boating. Wildlife biologists saw this occur with the related invasive zebra and quagga mussels after they initially were found in 2007 and 2008 in the lower Colorado River, Lake Mead and Lake Mohave. The pests are now also found in Southern California.
The concern with the golden mussel is that it’s much hardier and can survive in aquatic environments with more divergent calcium, pH, temperature and salinity levels than its relatives. Minute golden mussel veligers, or mussels in a free-floating immature stage, can survive and go undetected in as little as a capful of water.
That’s why one of the main management recommendations from the state multiagency 2025 Golden Mussel Framework is to clean, drain and dry all watercraft before entering a waterway and after pulling them out.
Many water districts took heed in 2025 and some went so far as closing all boat launches at their reservoirs to prevent mollusk infestations. The East Bay Municipal Utility District, for example, shut Pardee, Camanche and San Pablo reservoirs to boating unless the crafts were at permanent slips or on-site dry storage at the close of the 2024 season.
At its November 2025 meeting, the EBMUD Board of Directors voted to reopen Camanche and San Pablo reservoirs to recreational boating in 2026, provided trailered vessels pass inspection, undergo a mandatory 30-day quarantine and are affixed with a tamper-proof band. The district does not plan to reopen Pardee Reservoir this year.
“Due to its critical function as the primary water source for 1.4 million people, it will remain closed to protect the environment and vital infrastructure,” EBMUD spokesperson Nelsy Rodriguez said. The district plans to continue sampling for mussels monthly.
To help water districts and other boat facility operators, the California Department of Fish and Wildlife last September awarded about $1.3 million in grants for mussel-related boat inspections.
Known scientifically as Limnoperna fortunei, golden mussels are native to Southeast Asia. They likely hitchhiked in ship bilge water into the Stockton Deepwater Ship Canal and Port of Stockton, where they were confirmed in October 2024. Since then, they’ve spread and been found from the Sacramento River near Rio Vista to the Santa Ana Valley Pipeline south of Highway 60 in Riverside County.
They also have been detected in San Luis Reservoir, the Friant-Kern Canal, Westlands Water District pumps and in several places along the California Aqueduct.
Golden mussels average about 0.75 inches and get their name from the shell’s yellow to golden color. Their appearance is similar to zebra and quagga mussels. To differentiate the newcomer from the other two, wildlife experts use genetic testing or microscopic examination.
As filter feeders, golden mussels also can disrupt aquatic environments, deplete water’s oxygen levels and cause algae blooms. They begin reproducing at about 3 months old, reproduce year-round and release millions of eggs. As a result, they can quickly build populations, encrusting pipes, motors, boat hulls and other hard surfaces.
For now, researchers continue to study potential management measures, including ultraviolet light, molluscicides, copper, chlorine, and antifouling coatings and paints.
Kelly Stockton-Fiti, a Henderson, Nevada-based consultant who has spent 18 years studying invasive mollusks, said the challenge will be finding methods that target golden mussels without affecting other species. She spoke about invasive bivalves at the Association of California Water Agencies fall conference in December.
Part of Stockton-Fiti’s research has involved validating Zequanox, a microbial-based pesticide that disrupts the digestive systems of zebra and quagga mussels. Whether the product also is as effective against golden mussels has yet to be determined.
She said questions also remain about how long golden mussels can survive in a dry environment such as the watercraft dry-out period required by some water districts and the lethal temperature for hot-water cleaning.
“It takes time to come up with answers,” Stockton-Fiti said. “The best we can do is clean, drain and dry for now.”
To monitor the golden mussels’ spread, California wildlife officials ask people who think they’ve seen it to take a clear, close-up photo of it near an identifiable object, such as a coin or ruler, for scale. Fill out the golden mussel reporting form found at https://tinyurl.com/3jes9kwk and upload the image under the “Did you see mussels?” question.
Vicky Boyd is a reporter in Modesto. She can be reached at agalert@cfbf.com.
