Invasive Mussel News

Golden Mussel Detections in California

Martinez Reservoir

September 8, 2025 – juvenile mussels were discovered on a settlement plate in Martinez Reservoir, Contra Costa County. The reservoir is the terminal reservoir of the Contra Costa Canal and receives water from the Delta. The mussels were genetically confirmed as golden mussel by polymerase chain reaction (PCR) analysis and DNA sequencing.

Santa Ana Valley Pipeline

September 29, 2025 – golden mussel veligers were detected by cross-polarized light microscopy (CPLM) in plankton samples collected at two routine sampling locations on the Santa Ana Valley Pipeline located downstream of Silverwood Lake and the Devil Canyon Powerplant, San Bernardino County. The samples were collected on September 23rd and 29th. The veligers were genetically confirmed by PCR analysis and DNA sequencing.

DWR, in coordination with partner agencies, has implemented regular inspections and maintenance at State Water Project facilities to minimize the effects of golden mussels. The discovery of golden mussels poses no imminent impacts to water quality or DWR’s ability to deliver water to 27 million Californians. DWR continues to work diligently to implement protective measures to minimize the spread of this invasive species, prevent the fouling of equipment and maintain operational capacity. For specific questions about DWR’s response, please contact Maggie Macias, DWR Information Officer at (916) 902-7405. For questions regarding CDFW’s response, please contact CDFW’s hotline at (866) 440-9530.

Contra Loma Reservoir

October 7, 2025 – juvenile mussels were discovered on a settlement plate in Contra Loma Reservoir, Contra Costa County. The reservoir is part of the Central Valley Project and receives water from the Delta. The mussels were genetically confirmed as golden mussel by PCR analysis and DNA sequencing.

Golden Mussel Detections in California

Delta-Mendota Canal at Bass Avenue Bridge

September 17, 2025 – adult mussels were discovered in the Delta-Mendota Canal at the Bass Avenue Bridge in Mendota, Fresno County. The mussels were genetically identified as golden mussels using qPCR analysis.

San Luis Reservoir/Pacheco Pumping Plant

September 9, 2025 – golden mussel veligers were detected by cross-polarized light microscopy (CPLM) in a plankton sample collected at the Pacheco Pumping Plant, Merced County. The veligers were genetically identified via polymerase chain reaction (PCR) analysis and were negative for quagga/zebra mussels. Pacheco Pumping Plant draws water from San Luis Reservoir, Merced County. San Luis Reservoir receives water from O’Neill Forebay which is infested with golden mussel. For more information, read the October 3, 2025 news release.

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

• Golden mussel map
• Quagga/zebra mussel map

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)

On July 15, 2025, CDFW’s Invasive Species Program (ISP) laboratory staff detected a total of three suspected golden mussel (Limnoperna fortunei) veligers in plankton tow samples collected at Dock 25 in Lake Palmdale on June 26, 2025 and July 10, 2025. The veligers were confirmed by cross-polarized light microscopy (CPLM), polymerase chain reaction (PCR), and DNA sequencing for species confirmation.

Lake Palmdale, also known as Harold Reservoir, is a freshwater storage reservoir located near the City of Palmdale in the Antelope Valley in Los Angeles County, CA, and is owned and operated by the Palmdale Water District (PWD). The lake’s two water sources include the East Branch of the California Aqueduct (State Water Project) and Littlerock Reservoir. Water is stored in Lake Palmdale and eventually treated at PWD’s Leslie O. Carter Water Treatment Plant for distribution to the public, serving residents and businesses of the City of Palmdale and unincorporated areas of Los Angeles County.

Lake Palmdale receives water from the State Water Project’s East Branch and is the first detection of golden mussel on the East Branch. Multiple detections of golden mussel have been observed upstream of Lake Palmdale in the California Aqueduct.

For specific questions about Palmdale Water District’s response, please contact Scott Rogers, Assistant General Manager, at (661) 456-1020. For questions regarding CDFW’s response, please contact CDFW’s hotline at (866) 440-9530.

On July 7, 2025, Department of Water Resources staff found a single golden mussel attached to an intake stop log at John R Teerink Wheeler Ridge Pumping Plant. This pumping plant is located on the California Aqueduct near Mettler and it is the southernmost detection to date of an adult golden mussel in California. Water from the California Aqueduct flows south of here and splits into the East and West Branches of the Aqueduct. Water in the Western Branch of the Aqueduct flows into Quail Lake, where golden mussel veligers were detected in May and June 2025. Water from Quail Lake is released via the Lower Quail Canal, passes through the Warne Powerplant, and flows to Pyramid Lake. Water from Pyramid Lake flows into Elderberry Forebay, and Castaic Lake, which is the terminus of the West Branch. Water from Castaic Lake flows into Castaic Lagoon, Castaic Creek, and the Santa Clara River. Pyramid Lake also releases water to Middle Piru Creek which flows to Lake Piru, Lower Piru Creek, and Santa Clara River. Quagga mussels have been detected in Pyramid Lake and downstream waters.

Water in the East Branch of the Aqueduct flows into Silverwood Lake and Lake Perris. Lake Perris is the terminus of the East Branch.

In response to the detection of golden mussel in California waterways, the state of California has developed a comprehensive Golden Mussel Response Framework (PDF) to address this invasive species threat. DWR, in coordination with partner agencies, has implemented regular inspections and maintenance at State Water Project facilities to minimize the effects of golden mussels. The discovery of golden mussels poses no imminent impacts to water quality or DWR’s ability to deliver water to 27 million Californians.& DWR continues to work diligently to implement protective measures to minimize the spread of this invasive species, prevent the fouling of equipment, and maintain operational capacity.

For specific questions about DWR’s response, please contact Maggie Macias, DWR Information Officer at (916) 902-7405. For questions regarding CDFW’s response, please contact CDFW’s hotline at (866) 440-9530.