Invasive Mussel News

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  • June 30, 2025

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.

Categories: General
  • May 10, 2024

On April 9, California Department of Wildlife (CDFW) Invasive Species Program staff detected 12 veligers using cross-polarized microscopy in a plankton tow sample collected on February 23 at Castaic Lagoon, which is downstream of Castaic Lake. On April 10, CDFW staff also detected 33 veligers in a plankton tow sample collected on March 30 in Castaic Lagoon. The veligers in Castaic Lagoon have been confirmed to be quagga mussel via PCR and DNA sequencing.  

Castaic Lagoon is located near the unincorporated community of Castaic in Los Angeles County. It is immediately downstream of Castaic Lake and used for non-powered boating, canoeing, and swimming. Castaic Lake and Castaic Lagoon are part of the State Water Project and of the Castaic Lake State Recreation Area. The California Department of Water Resources (DWR) is the water manager for Castaic Lagoon and the Los Angeles Department of Parks and Recreation manages recreational access.

Adult quagga mussels were discovered in Castaic Lake in 2021. Pyramid Lake, known to have quagga mussels since 2016, is upstream of Castaic Lake. Castaic Lagoon is immediately downstream of Castaic Lake and has been presumed to be exposed to mussels.

Castaic Lagoon discharges to Castaic Creek, a tributary to the Santa Clara River. Quagga mussels were discovered in the Santa Clara River downstream of Castaic Creek below the confluence with Piru Creek in 2017.

For questions that are specific to 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.

Categories: General
  • February 10, 2023

On January 6, 2023, the Metropolitan Water District of Southern California (Metropolitan) detected a single quagga mussel veliger using cross-polarized microscopy in a large volume plankton net sample collected at Metropolitan’s Foothill Feeder Pressure Control Structure, which is downstream of Castaic Lake. The veliger was confirmed as a quagga mussel by PCR and DNA sequencing.

Adult quagga mussels were previously detected by the California Department of Water Resources in Castaic Lake in August 2021.

For questions specific to Metropolitan’s facilities and response, please contact Paul Rochelle, Water Quality Section Manager, at (909) 392-5155.

For questions regarding CDFW’s response, please contact CDFW’s hotline at (866) 440-9530.

Categories: General

Fisheries Branch
Branch Chief: Jay Rowan
1010 Riverside Parkway, West Sacramento, CA 95605
Fisheries@wildlife.ca.gov