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 12, Interstate 5, and Interstate 205 will added to the map. No notifications will be distributed via the Invasive Mussel News. To receive notices for signification detections, 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.