Introduction
Information regarding quagga / zebra mussel infestations in California will be posted on this web page. These discoveries are a developing situation; more information will be forthcoming and shared as it is available. Please refer to the Quagga and Zebra Mussel Sightings Distribution in California map (PDF) (opens in new tab) for the most up-to-date list of confirmed locations.
April 2024 - Castaic Lagoon
April 9, 2024 - Summary of Discovery
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.
November 2023 - Freeman Diversion Facility (source water Santa Clara River)
November 9, 2023 - Summary of Discovery
On November 9, 2023, United Water Conservation District (United) found 80 adult quagga mussels at the upstream end of United’s owned and operated Freeman Diversion Facility (Facility). Since November 9, 2023, United has completed additional visual and tactile surveys of the Freeman Diversion Facility and has found limited numbers of adult quagga mussels at several locations throughout the Facility.
The Facility is located near the unincorporated community of Saticoy in Ventura County, California, and is used to redirect water from the Santa Clara River to spreading basins for groundwater recharge. Quagga mussels were discovered in the Santa Clara River upstream of the Freeman Diversion Facility 2017.
For questions specific to United response, please contact Hannah Gacria-Wickstrum, United Water Conservation District, at HannahG@unitedwater.org, or Marissa Caringella, MarissaC@unitedwater.org. For questions regarding CDFW’s response, please contact CDFW’s hotline at (866) 440-9530.
February 10, 2023 - Summary of Discovery
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.
August 2021 - Castaic Lake
August 30, 2021 - Summary of Discovery
On August 6, 2021, a Castaic Lake park visitor reported finding one adult quagga mussel while kayaking in Castaic Lake (Los Angeles County). The specimen was sent to California Department of Fish and Wildlife (CDFW) for laboratory analysis which confirmed via genetic analysis the species identification as quagga mussel.
On August 17, 2021, Department of Water Resources (DWR) and CDFW staff discovered a ½ shell (dead) quagga mussel and a full shell (dead) quagga mussel along the shoreline of Castaic Lake.
On August 24, 2021, CDFW staff discovered a full shell (dead) quagga mussel along the shoreline of Castaic Lake.
These discoveries constitute the detection of adult mussels at Castaic Lake, thereby triggering management actions be taken to control mussels within the system.
Pyramid Lake, known to have quagga mussels since 2016, is upstream of Castaic Lake. Castaic Lagoon is immediately downstream of Castaic Lake, and therefore is presumed to be exposed to mussels.
To date, DWR and CDFW have not detected larval veliger-stage mussels in Castaic Lake during routine monitoring. CDFW will continue to work with DWR to delineate the population.
DWR, the owner and operator of Castaic Lake, is taking steps to implement a containment program. Los Angeles Department of Parks and Recreation, the recreation manager, began implementing exit inspections at Castaic Lake on August 13, 2021, to prevent the movement of quagga mussels. Boaters at these waterbodies, as well as all other waterbodies, should continue to clean, drain, and dry their watercraft and equipment after every visit.
For questions that are specific to DWR’s response, please contact Maggie Macias, DWR Information Officer, (916) 820-7662. For questions regarding CDFW’s response, please contact CDFW’s hotline at (866) 440-9530.
August 30, 2021 - News release (Department of Water Resources)
Quagga Mussel Discovery at Castaic Lake: Boating Requirements Implemented (opens in new tab) SACRAMENTO, Calif. – The California Department of Water Resources (DWR) will begin implementing additional boating requirements at Castaic Lake in Los Angeles County due to the recent discovery of invasive quagga mussels...
May 2021 - Santa Margarita River
May 20, 2021 - Summary of Discovery
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. Adults were detected downstream
of the WR-34 discharge site. No adults were discovered above that location. 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.
October 2017 - Upper San Gabriel River
October 27, 2017 - Summary of Discovery
On October 27, 2017, the Metropolitan Water District of Southern California (MWD) notified the California Department of Fish and Wildlife (CDFW) that MWD had been delivering raw water from the East Branch of the State Water Project (SWP) through the Rialto Pipeline and the Glendora Tunnel to its USG-03 service connection since August 3, 2017. This water is released into the upper San Gabriel River and then flows through the natural riverbed and concrete-lined channels into the San Gabriel Canyon and Santa Fe Spreading Grounds operated by the Los Angeles County Department of Public Works (LACDPW) for groundwater recharge.
On October 25, 2017, MWD detected quagga mussel veligers at the USG-03 service connection. Veligers were identified by MWD using microscopy and confirmed by PCR and DNA sequencing. Additional veligers were detected at USG-03 on October 26, 30, and 31, and in the upper San Gabriel River on October 26 and 31. Downstream agencies and the LACDPW were notified by MWD immediately and water delivery at USG-03 was stopped on October 31.
An operational review clearly indicates that these veligers originated from Colorado River Aqueduct (CRA) supplies and not from the SWP. An unplanned operational issue resulted in CRA water flowing into the Glendora Tunnel, mixing with the SWP supply, and being released at USG-03 for approximately 12 days. At the time of release, all of the river flow was diverted into LACDPW’s Santa Fe Spreading Grounds and no downstream waterbodies were impacted by this release.
Upon learning of the release, MWD immediately implemented a control and mitigation plan in cooperation with multiple water agencies and the LACDPW. These measures included flushing and chlorinating the affected pipelines, and desiccating the groundwater recharge basins. Monitoring of multiple downstream locations has shown no veliger detections since the initial sightings on October 26 and 31, 2017. This was a transient event and there is currently no evidence of quagga mussels in the San Gabriel River.
All released water from Morris Dam and USG-3 will be fully contained by the LACDWP’s rubber dam and diverted into the Santa Fe Spreading Grounds facility until follow-up monitoring can be conducted to determine whether mussels have spread to the San Gabriel River.
For questions that are specific to MWD, please contact Paul Rochelle, Microbiology Unit Manager, at (909)392-5155. For questions regarding CDFW's response, please contact CDFW's hotline at (866) 440-9530.
October 2017 - Lower Piru Creek
October 17, 2017 - Summary of Discovery
On October 17, 2017, United Water Conservation District (UWCD) notified the California Department of Fish and Wildlife (CDFW) that their staff discovered 18 adult quagga mussels on cobbles in the Lower Piru Creek, Ventura County, approximately ¼ mile upstream of the confluence with the Santa Clara River. CDFW staff have visually identified the specimens as quagga mussels.
Lake Piru releases water into Lower Piru Creek. Lower Piru Creek flows into the Santa Clara River approximately 6 miles below Lake Piru’s Santa Felicia Dam. Adult mussels were discovered in Lake Piru in December 2013. In January 2014, adult mussels were discovered in Lower Piru Creek, below the Santa Felicia Dam. In August 2017, adult mussels were discovered in Santa Clara River downstream of the confluence with Lower Piru Creek.
For questions that are specific to UWCD, please contact Anthony Emmert, Deputy General Manager, UWCD, at (805) 525-4431. For questions regarding CDFW's response, please contact CDFW's hotline at (866) 440-9530.
August 2017 – Santa Clara River
August 30, 2017 - Summary of Discovery
On August 23, 2017, United Water Conservation District (UWCD) notified the California Department of Fish and Wildlife (CDFW) that their staff had surveyed six locations along the Santa Clara River downstream of the confluence of Lower Piru Creek, Ventura County. Their staff discovered one adult quagga mussel on the Torrey Road Bridge, Piru, California, and twelve adult quagga mussels on the 12th Street Bridge, Santa Paula, California. UWCD reported that all quagga mussels detected during the surveys were attached to vertical structures in shaded areas with slow-flowing to still water. UWCD did not discover mussels at any of the other four locations surveyed. UWCD and CDFW have visually identified the specimens as quagga mussels.
CDFW staff surveyed a portion of the Santa Clara River on August 26, 2017. CDFW did not discover mussels at the location surveyed. A plankton sample was collected and sent to CDFW's laboratory for analysis; sample results were negative.
For questions that are specific to UWCD, please contact Anthony Emmert, Deputy General Manager, UWCD, at (805) 525-4431. For questions regarding CDFW's response, please contact CDFW's hotline at (866) 440-9530.
February 2017 – Santa Ana Pipeline
February 24, 2017 - News release (Department of Water Resources)
Invasive Mussel Veligers Detected in the Santa Ana Pipeline; State Conducting Further Testing (PDF)
SACRAMENTO – Mussel veligers (microscopic, free-floating larval life stage) this month were detected in water samples collected at the North Park valve of the Santa Ana Pipeline, which transports water from Silverwood Lake, San Bernardino County, to Lake Perris, Riverside County. Further testing is under way by the California Department of Fish and Wildlife (CDFW) to confirm the findings and determine if the veligers are quagga mussels or zebra mussels...
December 2016 – Pyramid Lake, Angeles Tunnel, Castaic Power Plant, Elderberry Forebay, Castaic Lake, Castaic Lagoon
August 30, 2017 - Updated Information Regarding Discovery
On December 13, 2016, Department of Water Resources (DWR) and Metropolitan Water District of Southern California (MWD) staff inspected the Angeles Tunnel again and ten additional dead quagga mussels were detected. The mussels range from 13-33 mm, similar in size to the six mussels initially discovered on December 8. Staff also inspected the drainage water in the Pyramid Dam stream release access chamber and in Middle Piru Creek immediately below the dam; no mussels were detected. On December 14, 2016, DWR and MWD staff collected plankton tow samples on Pyramid and Castaic Lakes. Samples were sent to Scripps and MWD laboratories for analysis; sample results were all negative. At Pyramid Lake, staff also inspected spillway buoys, outlet tower buoys, settlement plates, and two Sherriff boats that were pulled from the water; no mussels were detected. At Castaic Lake, settlement plates and rocky shoreline near the inlet were inspected; no mussels were detected. The Los Angeles County Department of Parks and Recreation divers dove in Castaic Lake and inspected hard substrates such as buoys and anchor cables; no mussels were detected.
On December 20, 2016, remote operated vehicle (ROV) inspection of Pyramid Angeles Tunnel intake was inspected to a depth of approximately 300 feet. One mussel was observed and appeared to be alive.
On January 4, 2017, MWD inspected their Foothill Hydro Electric Plant just downstream of Castaic Lake. The plant has several strainers and filters that were removed, and their contents returned to the lab for inspection; no mussels were detected.
All subsequent sampling conducted to date has been negative.
On December 14, 2017 (not December 15, 2017 as previous reported), MWD and Los Angeles Department of Water and Power (LADWP) inspected the dewatered Elderberry Forebay. Two adult quagga mussels were discovered at the Castaic Power Plant at the northern end of Elderberry Forebay. Laboratory analysis conducted by MWD corroborated the visual species identification. MWD inspected the dewatered outlet tower and dam of the Elderberry Forebay; no mussels were detected.
December 16, 2016 - Summary of Discovery
On December 8, 2016, six adult quagga mussels were discovered by California Department of Water Resources (DWR) in the Angeles Tunnel, a pipeline that moves water from Pyramid Lake to Elderberry Forebay and subsequently Castaic Lake (Los Angeles County). Laboratory analysis conducted by CDFW corroborated the visual species identification made by DWR staff. Based on this discovery the California Department of Fish and Wildlife (CDFW) considers Pyramid Lake to be infested with quagga mussels.
On December 15, 2016, Metropolitan Water District of Southern California and Los Angeles Department of Water and Power (LADWP) discovered two adult quagga mussels at the Castaic Power Plant at the northern end of Elderberry Forebay, which is currently dewatered. Specimens have been sent for laboratory analysis to corroborate the visual species identification.
Given the connectivity of the waterbodies, CDFW presumes that Castaic Lake and Castaic Lagoon have been exposed to mussels and warrant management actions be taken comparable to those where adult mussels have been found.
DWR, the manager of Pyramid and Castaic lakes, and LADWP, manager of Castaic Power Plant and Elderberry Forebay, are implementing actions to contain the infestation and managing exiting watercraft to prevent the movement of quagga mussels and infested water. DWR and local agencies are conducting additional surveying to determine the extent of the infestation. CDFW will continue to work with DWR and LADWP to delineate the infestation and develop a control plans for the infested waterbodies.
Boaters at these waterbodies, as well as all other waterbodies, should continue to clean, drain, and dry their watercraft and equipment after every visit. Waterbodies with prevention programs screening for high-risk watercraft should consider Pyramid Lake, Elderberry Forebay, Castaic Lake, and Castaic Lagoon infested waters and manage watercraft originating from these waterbodies accordingly.
For questions that are specific to DWR’s response, please contact Doug Carlson, DWR Information Officer, (916) 653-5114 or Ted Thomas, DWR Information Officer, (916) 653-9712. For questions regarding CDFW’s response, please contact CDFW’s hotline at (866) 440-9530.
December 15, 2016 - News release (Department of Water Resources)
Quagga Mussel Infestation Triggers Boating Restrictions at Pyramid and Castaic Lakes (PDF) SACRAMENTO – Boats leaving Pyramid Lake and Castaic Lake are subject to restrictions to help prevent the spread of quagga mussels, which were discovered last week in a tunnel that connects the two Los Angeles County lakes, the California Department of Water Resources (DWR) announced today...
December 9, 2016 - News release (Department of Water Resources)
Quagga Mussel Infestation Discovered in Pyramid Lake; State Imposes Boating Restrictions (PDF) (opens in new tab) SACRAMENTO – The Quagga Mussel is a small, non-native freshwater mollusk that the Department of Water Resources (DWR) had successfully prevented from infesting the State Water Project (SWP) since the species was first discovered in California in 2007. However, on December 8, six adult quagga mussels were found in the Angeles Tunnel, which serves as a connector between Pyramid Lake and Elderberry Forebay, two SWP components north of Los Angeles...