Adult Quagga Mussels Detected in the Santa Margarita River
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.