Invasive Mussel News

The California Department of Fish and Wildlife Invasive Species Program is forwarding the following news release from the California Department of Water Resources.

New Boating Protocols Implemented and Effective Immediately at Silverwood Lake

SACRAMENTO, Calif.— The Department of Water Resources (DWR), California Department of Fish and Wildlife (CDFW), and California State Parks have confirmed presence of the invasive golden mussel at Pyramid Lake in Los Angeles County and Silverwood Lake in San Bernardino County. These lakes are the southernmost State Water Project (SWP) reservoirs where golden mussels have been detected. The invasive species was recently discovered during a routine water test by DWR; in response, State Parks has updated Silverwood Lake’s boat inspection protocols, effective immediately. Pyramid Lake, which is managed by DWR, implemented exit inspections following the discovery of quagga mussels in 2016.

The golden mussel, native to China and Southeast Asia, was initially detected in the Sacramento-San Joaquin Delta and O’Neill Forebay in October 2024 and has subsequently spread south. This small freshwater bivalve is known for its rapid reproduction and ability to clog water infrastructures, disrupt ecosystems, and outcompete native species. These invasive mussels can also cause significant damage to boats by attaching to hulls and clogging engines, leading to increased costs for boaters and other motorized vessel owners. Currently, there are no effective methods to treat or eliminate the golden mussel from infested waterways, making prevention of further spread to non-infested waterways a top priority.

Through a series of coordinated actions with state and local partners, DWR has expanded its activities to protect SWP facilities against this destructive species while maintaining operational capacity to deliver water to 27 million Californians and 750,000 acres of farmland. Actions to mitigate the spread of golden mussels include ongoing research to better understand and suppress the species, as well as designing and implementing new measures to protect pumping plants, hydroelectric plants, and water supply deliveries.

New Boating Protocols at Silverwood Lake

Due to the confirmed presence of golden mussels in Silverwood Lake, the following changes to boating protocols are now in effect:

• Vessel inspections upon arrival are discontinued: As the lake is now infested with golden mussels, mandatory inspections for invasive mussels upon entry are no longer required.
• Drain plug removal/outbound inspection: Drain plugs should be pulled on all vessels prior to exiting Silverwood Lake to prevent the transport of lake water, which may contain microscopic golden mussel larvae or veligers.
• Clean and dry advisory: Boaters are strongly advised to ensure their vessels are thoroughly cleaned, drained, and dried after recreating on Silverwood Lake. For vessels that cannot be completely drained of water, such as boats with ballast tanks, boaters are advised to check with the specific body of water they plan to recreate for decontamination guidelines before launching in other lakes or bodies of water not yet infested with invasive mussels. These measures aim to reduce the risk of spreading golden mussels to other California waterways not impacted by invasive mussels. A list of reservoirs contact and watercraft inspection information.

Potential Impact on Lake Perris

While nearby Lake Perris State Recreation Area (SRA) has not yet tested positive for golden mussels, the daily transfer of millions of gallons of water from Silverwood Lake to Lake Perris, combined with the invasive mussel’s rapid reproduction, makes the spread to Lake Perris highly likely. Monitoring efforts are ongoing, and the public will be notified of any updates. Lake Perris is continuing inspections for now and will discontinue incoming inspections if Lake Perris tests positive for golden mussels and will adopt this exit inspection protocol.

For more information on invasive species prevention or to report suspected sightings of golden mussels, visit the CDFW’s Invasive Species Program, call (866) 440-9530 or email invasives@wildlife.ca.gov.

Learn more about DWR's SWP golden mussel mitigation efforts.

Contacts:

• Newsroom@parks.ca.gov
  California State Parks
• media@water.ca.gov
  California Department of Water Resources

Golden Mussel Detections in California

Sacramento-San Joaquin Delta

Rio Vista: July 1, 2025 – golden mussel veligers were detected by cross-polarized light microscopy (CPLM) in a plankton sample collected in the Sacramento River near Rio Vista, Solano County. The veligers were genetically identified via polymerase chain reaction (PCR) analysis. On September 4, 2025, one adult golden mussel was detected at the same location and genetically identified via PCR analysis.

New Bridge Marina: July 29, 2025 – three adult mussels were discovered on the underside of the slips at New Bridge Marina by the Highway 160 Bridge in Antioch, Contra Costa County. The mussels were genetically identified as golden mussel using PCR analysis and DNA sequencing.

Pittsburgh Yacht Club: July 29, 2025 – one mussel was discovered on the underside of a slip at Pittsburgh Yacht Club in Pittsburgh, Contra Costa County. The mussels were genetically identified as golden mussel using PCR analysis and DNA sequencing.

South Delta: September 3, 2025 – adult mussels were discovered in Grant Line Canal and at two sites in the Upper Old River. All 3 sites are in San Joaquin County. The adult mussels were morphologically identified.

Pirates Lair Marina: September 4, 2025 – adult mussels were discovered at Pirate Lair Marina, Sacramento County, attached to docks. The adult mussels were morphologically identified.

San Joaquin River: September 4, 2025 – 100+ juvenile mussels were detected in San Joaquin River downstream of Mossdale Crossing, San Joaquin County, attached to flow monitoring equipment. The mussels were morphologically identified.

Patterson Pass Water Treatment Plant

August 14, 2025 – a single adult golden mussel was discovered in a strainer on a raw water sample line during routine cleaning at the Patterson Pass Water Treatment Plant in Livermore, Alameda County. The veligers were genetically identified via PCR analysis and DNA sequencing.

Chrisman Wind Gap Pumping Plant

August 22, 2025 – 25 adult golden mussels were discovered on the man doors of pump units at Chrisman Wind Gap Pumping Plant (just south of Wheeler Ridge Pumping Plant on the California Aqueduct), Kern County. The adult mussels were morphologically identified.

Silverwood Lake

August 26, 2025 – a golden mussel veliger was detected by CPLM in a plankton sample collected at the Silverwood Lake outlet. The veligers were genetically identified via PCR analysis and negative for quagga/zebra mussels.

Pyramid Lake

August 28, 2025 – adult golden mussels were discovered in Pyramid Lake, Los Angeles County, attached to settlement plates located at the William E. Warne Powerplant. Quagga mussels were also attached to the settlement plates. The mussels were genetically identified as golden mussel using PCR analysis. Sequencing results are pending. Quagga mussels were first detected in Pyramid Lake in 2016.

For a map of all confirmed detections of invasive mussels visit:

• Golden mussel map
• Quagga/zebra mussel map (PDF)

The California Department of Fish and Wildlife Invasive Species Program is forwarding the following notice from the Pacific States Marine Fisheries Commission

2025-2026 WID Training Announcement

We are pleased to share the upcoming schedule for virtual watercraft inspection and decontamination (WID) classes. There is no cost to attend but registration is required. Click on the dates below to sign up. Once registered, more information will be sent to you via email.

Level 1 or 2 (Inspection and Decontamination) Classes:

• September 4 – 5, 2025
• September 30 – October 2, 2025
• November 4 – 6, 2025
• December 9 – 11, 2025
• January 13 – 15, 2026
• February 10 – 12, 2026
• March 10 – 12, 2026
• April 14 – 16, 2026
• May 5 – 7, 2026

For more information, please visit the WID Training Website.
Questions? Please contact Elizabeth Brown at elizabeth@widtraining.com.