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Dreissenid Mussels Discovered in Lake Piru in Ventura County

CDFW press release
Dreissenid mussels (quagga or zebra) have been discovered in Lake Piru in Ventura County. The California Department of Fish and Wildlife (CDFW) is working with United Water Conservation District and Lake Piru Recreation Area staff to contain the infestation. All boaters are being required to clean, drain and dry their watercraft upon exit from the lake. This discovery marks the first time quagga or zebra mussels have been found in a Southern California waterbody that does not receive water from the Colorado River.

On Dec. 18, Lake Piru Recreation Area staff reported the discovery of potential quagga mussels to CDFW. The mussels were found attached to a Lake Piru patrol boat and several additional mussels were subsequently found on devices deployed in the lake for the purpose of detecting mussels and on the shoreline. CDFW staff tentatively identified the mussels, which range in size from one half to three quarter inches long, as quagga. Genetic testing is underway to confirm this identification. Lake Piru Recreation Area staff are working to determine the full extent of the infestation.

Lake Piru, which is managed by United Water Conservation District, is located downstream of Pyramid Lake. Lake Piru drains into Lower Piru Creek, a tributary of the Santa Clara River.

Quagga and zebra mussels, non-native freshwater mussels native to Eurasia, multiply quickly and encrust watercraft and infrastructure, and compete for food with native and sport fish species. These mussels can be spread from one body of water to another attached to nearly anything that has been in an infested waterbody, or via standing water from an infested waterbody entrapped in boat engines, bilges, live-wells and buckets. People who launch vessels at any body of water are subject to watercraft inspections and are encouraged to clean, drain and dry their motorized and non-motorized boats, including personal watercraft, and any equipment that comes into contact with the water before and after recreating at a waterway.

For more information on boat inspection programs and preventing the spread of quagga and zebra mussels visit CDFWs website (

Quagga mussels were first detected in the Colorado River system in January 2007 and were later found in San Diego and Riverside counties. They are now known to be in 26 waters in California. Zebra mussels were discovered in San Justo Reservoir in San Benito County in January 2008.

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