Invasive Mussel News

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  • July 21, 2025

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.

Categories: General
  • June 2, 2021

On May 20, 2021, Rancho California Water District (RCWD) notified the California Department of Fish and Wildlife (CDFW) that RCWD discovered adult quagga mussel in the Santa Margarita River, Riverside County, approximately 1,000 feet downstream from the San Diego Pipeline #5 WR-34 Discharge Site. San Diego Pipeline #5 transports water from Lake Skinner, a lake known to have quagga mussels (Dreissena rostriformis bugensis) since August 2007. Water from Lake Skinner is chlorinated, transported via San Diego Pipeline #5, then de-chlorinated at the WR-34 Discharge Site before being discharged into the Santa Margarita River. Metropolitan Water District of Southern California (MWD) manages Lake Skinner, the chlorination, and the pipeline, while RCWD manages the dichlorination and discharge into the Santa Margarita River.

Santa Margarita River is west of the CA I-15 Highway in Temecula. Murrieta Creek and Temecula Creek merge to form the Santa Margarita River. The WR-34 Discharge Site is located just below the confluence of Murrieta Creek and Temecula Creek, and flows directly into the Santa Margarita River.

On May 21, CDFW Region 5 and 6 staff conducted surface surveys for presence/absence of mussels in Murrieta Creek working downstream to the Upper Santa Margarita River to the WR-34 discharge site. CDFW laboratory has visually identified the specimens as quagga mussels and confirmed that identification with PCR analysis. CDFW staff will conduct additional surface surveys in Santa Margarita River and at Lake O’Neill.

In December 2014, the US Bureau of Reclamation (USBR) notified CDFW of a positive detection from an October plankton tow sample collected near the same area of the Santa Margarita River. Follow up sampling by USBR, CDFW, and MWD in 2015 confirmed the presence of veligers in multiple samples, and several unpreserved samples were examined and no veligers exhibited movement. In June 2017 CDFW analyzed samples collected by RCWD and no mussels were detected.

For questions that are specific to RCWD, please contact Eva Plajzer, P.E., Assistant General Manager, RCWD, at (951) 296-6910. For questions regarding CDFW's response, please contact Dominique Norton at (916) 203-4499.

Categories: General

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