SACRAMENTO, California – The California Department of Water Resources (DWR), in coordination with California Department of Fish and Wildlife (CDFW) and California State Parks, is highlighting new measures to protect California’s water infrastructure and slow the spread of invasive golden mussels following a recent discovery of the species at San Luis Reservoir in Merced County.
San Luis Reservoir, the largest off-stream reservoir in the nation, is part of the San Luis Joint-Use Complex that serves the State Water Project (SWP) and federal Central Valley Project. The invasive species was recently discovered at the facility during a routine water test conducted by DWR. In response, mandatory watercraft inspections of all vessels leaving San Luis Reservoir are now in place and will help prevent the spread of mussel to other lakes and reservoirs.
Golden mussels, an invasive species detected in North America in October 2024, pose a threat to infrastructure and the ecological health of all state waterways. While the mussels pose no immediate threat to water quality or supplies, if left unchecked, they can compromise water delivery systems by clogging pipelines, screens, and filters.
To help reduce the risk of mussel colonization, DWR has implemented routine inspections of SWP facilities and expanded its efforts by applying new strategies to protect pumping plants, hydroelectric plants, and water supply deliveries.
The department will be installing medium-pressure ultraviolet light disinfection systems at several facilities to prevent mussel settlement in small-diameter piping of cooling water and fire protection water systems. DWR staff are also researching the use of low-dose chlorine, copper, and hot water to control mussel settlement in pipelines and on fish screens.
To date, golden mussels have not been detected at the SWP’s Oroville or Upper Feather River Lakes facilities. A new mapping tool developed by CDFW is now available online that shows the latest golden mussels detections in California.
Boaters and recreationists can also do their part in combating the spread of invasive mussels by following mandatory watercraft inspections of all vessels leaving SWP reservoirs, and remembering to “clean, drain, and dry” their watercraft before entering and leaving waterways. DWR’s new video series provides information about golden mussels, tips on how boaters can stop the spread, and what to expect during a mussel inspection.
State Parks’ Division of Boating and Waterways (DBW) maintains a list of its reservoir contacts, and the public is urged to visit State Parks DBW website to check current information on inspections or restrictions before heading out to recreate on the water. DBW also provides boaters and water body managers with up-to-date information through its invasive mussels page.
To report suspected golden mussel sightings or learn more about invasive species prevention, visit CDFW’s golden mussel page, call (866) 440-9530 or email invasives@wildlife.ca.gov. More information about the state’s coordinated efforts to combat golden mussels can be found in California’s comprehensive Golden Mussel Response Framework (PDF).
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