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.

Golden Mussel Detections in California, October 2024-June 2025

October 17, 2024 – Golden mussel (Limnoperna fortunei), an invasive, non-native freshwater bivalve, was discovered in the Sacramento-San Joaquin Delta (Delta). This is the first known detection of golden mussel in North America. Waters that are downstream of the Delta are presumed to be exposed to golden mussel.

The mussels were found attached to a float near the Port of Stockton by the California Department of Water Resources (DWR) and immediately reported to the California Department of Fish and Wildlife (CDFW). No mussels had been observed on the float in the prior months’ inspection. The mussels were sent to the UC Davis Genomic Variation Laboratory and the California Department of Food and Agriculture’s (CDFA) laboratory for identification. On October 23 and 24 UC Davis and CDFA independently returned genetic analysis results consistent with golden mussel.

Following the initial discovery of golden mussels in the Port of Stockton, observations of additional mussels were made at numerous locations throughout the Delta on water quality monitoring equipment and artificial substrates (deployed for the purpose of detecting invasive mussels.) Historical statewide quagga/zebra mussel and golden mussel early-detection monitoring is ongoing, and would be effective for detecting golden mussel.

October 25, 2024 – State Parks reported adult mussels on an artificial substrate deployed for monitoring for the presence of quagga/zebra mussels in O’Neill Forebay. Specimens collected from O’Neill Forebay were later confirmed to be golden mussel by genetic analysis conducted by UC Davis and CDFA labs.

October 31, 2024 – A multi-agency press release was published.

November 22, 2024 – DWR found an adult golden mussel on the louvers of the Skinner Fish Facility, just downstream of Clifton Court Forebay. The mussel was visually identified as a golden mussel by DWR. The Skinner Fish Facility is located at the entrance to the California Aqueduct. The facility works to divert fish away from the pumps that lift water into the California Aqueduct.

December 18, 2024 – US Bureau of Reclamation (USBR) discovered upwards of 20 adult mussels on the Tracy Fish Facility louvers, downstream of Clifton Court Forebay. The mussels were visually identified as golden mussel by USBR. The facility is located at the entrance to the Delta Mendota Canal, and it intercepts fish and diverts them away from the pumps that lift water into the canal.

December 30, 2024 – DWR reported adult mussels on an artificial substrate deployed in Bethany Reservoir. No mussels had been observed in the prior months’ inspection. DWR staff visually identified the species as golden mussel.

February 12, 2025 – DWR detected 3 adult golden mussels in a drained discharge pipe at the Las Perillas Pumping Plant. Subsequently, DWR inspected the pipe and found and removed several hundred mussels ranging in size from 0.7 to 2.2 cm. The Las Perillas Pumping Plant is a facility of the State Water Project (SWP) that is part of the Coastal Branch Aqueduct and located about one mile from the California Aqueduct near Avenal in Kings County. It lifts water from the aqueduct for delivery through the first 15 miles of the Coastal Branch. Water undergoes a conventional water treatment process at the Polonio Pass Water Treatment Plant (PPWTP). This conventional water treatment process includes flocculation, sedimentation, filtration, and disinfection with chlorine. This process is an effective built-in control to remove golden mussel veligers from source water and prevent passage further downstream. However, there is a water diversion upstream of the treatment plant that delivers untreated water from the Coastal Branch to Lake Evans and Lake Woollomes in Kern County.

February 26, 2025 – DWR detected an adult mussel in the backflush debris filter at Dos Amigos Pumping Plant. DWR visually identified the species as golden mussel. The Dos Amigos Pumping Plant is a facility of the State Water Project (SWP) that is part of the California Aqueduct. It is located about 15 miles downstream from Check 13, the outlet of O’Neill Forebay.

March 20, 2025 – DWR detected multiple adult golden mussels at Check 24 of the California Aqueduct. DWR visually identified the species as golden mussel. Check 24 is located near the junction of Highway 46 and Interstate 5. This is the southern-most sighting of golden mussels in the SWP to-date. The California Aqueduct delivers water to reservoirs throughout Southern California.

April 11, 2025 – Three adult mussels were discovered in the discharge pipeline at Pleasant Valley Pumping Plant. The mussels were sent to CDFW and were genetically identified as golden mussel. Pleasant Valley Pumping Plant draws water from a canal that is connected to the California Aqueduct. It is located about a mile and a half from the California Aqueduct.

April 30, 2025 – Westlands Water District reported more than 100 adult mussels on a pump at a pumping plant on the San Luis Canal. The mussels were sent to CDFW and were genetically identified as golden mussel. The San Luis Canal is a segment of the California Aqueduct that extends from south of O’Neill Forebay to Kettleman City in Kings County.

New confirmed golden mussel detections within the bounds of Highway 160, Highway 12, Interstate 5, and Interstate 205 will added to the map; however notifications will not be distributed via the Invasive Mussel News. To receive notices for significant detections beyond these bounds, subscribe to the Invasive Mussel News.

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For a list and map of all confirmed detections of invasive mussels visit:
Golden mussel map
Quagga/zebra mussel map

Report invasive mussel detections to CDFW’s online at Invasive Species Program, email invasives@wildlife.ca.gov, or call (866) 440-9530. Please include the specific location of the observation, and at least one clear close-up photograph of the organism, and your contact information.

Hello Water Managers,

This is a friendly reminder that Division of Boating and Waterways' Quagga and Zebra Mussel Infestation Prevention grant period close tomorrow, April 18, 2025 at 5 p.m. If you submitted your grants early, we encourage you to review your submission for completeness.

Thank you!

California Department of Fish and Wildlife (CDFW), Department of Water Resources, and California State Parks issued a joint press release on April 16, 2025 titled "California Takes Action to Halt Golden Mussel Invasions” announcing the development of a comprehensive Golden Mussel Response Framework developed by the Golden Mussel Task Force.

In addition, the California Department of Fish and Wildlife (CDFW) is offering $1 million in grant funding to boating facility operators to enhance efforts against invasive mussels, particularly the threat of golden mussels. This funding supports projects that help prevent the introduction and spread of invasive mussels in lakes, reservoirs and waterways, ensuring the long-term health of state waters. The grant solicitation and application link can be found on CDFW’s website.

California Department of Fish and Wildlife is relaying the following information received from the California Department of Food and Agriculture (CDFA). CDFW anticipates the following changes to CDFA's Border Protection Stations program operations will impact the interdiction and inspection of overland conveyances that may carry invasive mussels. Questions can be directed to CDFW via Invasives@wildlife.ca.gov or (866) 440-9530 and will be shared with CDFA.

The following information is being forwarded on behalf of the CDFA:

The State of California is currently facing a significant and ongoing budget deficit, and programs across CDFA are being required to implement budget reductions. In accordance with the budget reductions, the Border Protection Stations (BPS) Program will be reducing scheduled staffing levels to the minimum necessary to maintain safe operations for all working shifts, and will be reducing the hours of operation at multiple stations.

The following schedules of operation will be implemented effective April 1, 2025:

• Alturas: Open daylight hours
• Benton: Open daylight hours
• Blythe: Open 24/7
• Dorris: Open 24/7
• Hornbrook: Open 24/7
• Long Valley: Open 24/7
• Meyers: Open 8 hours per day
• Mt. Pass: Open 24/7
• Needles: Open 24/7
• Redwood Highway: Open daylight hours
• Smith River: Open daylight hours
• Topaz: Open 8 hours per day
• Truckee: Open 24/7
• Tulelake: Open daylight hours
• Vidal: Open 24/7
• Winterhaven: Open 24/7

For the stations open during daylight hours, they will be open for two shifts, which may vary seasonally from 14-16 hours.

Additionally, all stations are being instructed to focus on commercial traffic, with a primary focus on the compliance of high-risk agricultural commodities and the Program’s responsibilities for its cooperative agency agreements. Private vehicle inspections will be impacted by the reduced staffing levels, and should continue to be conducted as traffic and/or staffing allows.

And while all stations will continue to be scheduled for operation seven days per week, with the reduced available staffing there may be days where Station Managers will need to close operations for a day to ensure the safety of both program staff and the traveling public.

This message is being forwarded on behalf of California State Parks, Division of Boating and Waterways:

Save-The-Date Grant Announcement

California State Parks Division of Boating and Waterways (DBW)

QZ Grant Program has the following announcement:

The application period for the 2025 cycle will open on March 10, 2025 and will close on April 18, 2025 at 5:00 p.m. Up to $2M is expected to be awarded, pending available funding. If a reservoir is currently covered by a two-year 2024 QZ Grant, that reservoir will not be considered for a QZ Grant until the 2026 solicitation.

A presentation will be conducted via MS Teams on March 13, 2025; information will be posted on our webpage at: QZGrant@parks.ca.gov. The 2025 QZ grants are expected to begin in August, and will span two years.

Minimum Eligibility Requirements:

Grant applicant must own/manage any aspect of the water in a reservoir; The reservoir must be open to the public for recreation; and Grant applicant must demonstrate that the reservoir is uninfested with dreissenid mussels

To demonstrate that the reservoir is uninfested, applicants must provide mussel monitoring data collected since March 2024. Monitoring data can be from surface surveys, artificial substrates, and plankton tows.

Tier 2 Implementation Grant:

To be eligible for an implementation grant, applicants must provide a letter from the California Department of Fish and Wildlife (CDFW) at the time of application that states CDFW has reviewed and accepted a prevention plan for the reservoir (per Fish and Game Code Section 2302 and California Code of Regulations, Title 14, Section 672.1(b)).

Tier 1 Planning and Assessment Grant:

Applicants that do not already have a CDFW-accepted prevention plan can apply for a planning and assessment grant in order to develop a CDFW-accepted prevention plan for the reservoir.

For questions regarding quagga/zebra mussel monitoring, or for prevention planning, including how to obtain a letter from CDFW, contact CDFW at Invasives@wildlife.ca.gov or Telephone: (866) 440-9530.

Additional information will be sent prior to opening of the grant application window. This notice will also be posted on the DBW website.