NORTHERN CALIFORNIA — The discovery of an invasive species of mussel in the Sacramento-San Joaquin Delta has officials concerned and looking for potential impacts for other water bodies that are part of the delta water system, including Clear Lake.

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.

The water from Clear Lake drains into the delta through Cache Creek and the Yolo Bypass.

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, California State Parks, California Department of Water Resources, 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.

Angela DePalma-Dow, invasive mussel coordinator for Lake County Water Resources, told Lake County News that more information about the mussels is being put together so that agencies, partners, and the public have more of a clear idea of what to be on the lookout for when it comes to the golden mussels.

She said the population seems to be established at the site detected, so the impact as an invasive species to California waterways has merit.

DePalma-Dow said golden mussels are similar in shape and size as quagga and zebra mussels except without the stripes, but they have potential to cause just as much damage if introduced into freshwater lakes and streams.

“While they are named ‘golden’ they really are a brown-tannish but can look ‘shiny’ or ‘shimmery’ in the light,” DePalma-Dow said.

“The conditions the mussel likes to inhabit are like other invasive mussels except for depth,” she said. “Golden mussels can tolerate a little bit more salinity for up to about 10 days, which is very concerning since many boaters come from the Delta before visiting Clear Lake.”

The good news, said DePalma-Dow, is that the golden mussel doesn’t like to be too deep, and prefers water shallower than 10 meters, whereas the quagga and zebra mussels have been observed in depths from shallow zones all the way to 50 to 90 meters in the Great Lakes area.

“If this mussel is introduced into Clear Lake, or any other Lake County waterbody, there is an expectation for significant negative impact and damage to occur, however, lucky for us we have a great prevention program in place that if maintained (current state grants are unpredictable), can help prevent the introduction of these, and other concerning invasive species, into Clear Lake,” DePalma-Dow said.

“Making sure boaters are participating in the Lake County Invasive Mussel Prevention local sticker program is key,” she added. “Boaters can easily get their vessels screened and inspected, if needed, because this is imperative to preventing introductions of unwanted aquatic species. This program will work for the prevention of Golden Mussels too! Every boat and boat operator, including personal watercrafts, kayaks, canoes, and fisherpersons, should Clean, Drain, Dry, their boats and gear between visits to different waterbodies – every waterbody, every time!”

If anyone has any questions about mussel prevention in Lake County, they can visit www.nomussels.com or call Water Resources at 707-263-2344.

DePalma-Dow also urged people to visit these links from the U.S. Fish and Wildlife Service and the National Oceanic and Atmospheric Administration to get more information specifically for golden mussels.

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 This email address is being protected from spambots. You need JavaScript enabled to view it..
• 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.