Invasive Golden Mussels Hit Silverwood, Pyramid Lakes in SoCal

Invasive golden mussels found at Silverwood, Pyramid lakes — a new threat to Southern California water infrastructure

Invasive golden mussels have been confirmed at Silverwood Lake and Pyramid Lake, marking the southernmost detections in California’s State Water Project and prompting immediate inspection, containment and operational changes to protect infrastructure, ecosystems and recreation across Southern California.

Discovery and spread

Golden mussels (Limnoperna fortunei) are small, fast-breeding freshwater mussels native to Asia. They were first discovered in California in October 2024 in the Sacramento‑San Joaquin Delta and O’Neill Forebay and have spread rapidly, with state officials confirming positive samples at Silverwood and Pyramid lakes in September 2025. For official details see the California Department of Water Resources news release and the California Department of Fish and Wildlife notice.

The mussel spreads both as microscopic larvae (veligers) that move freely in water and as juveniles/adults attached to hard surfaces. Known pathways include trailering of boats and State Water Project transfers — mechanisms likely responsible for the downstate expansion (see KPBS reporting).

Impact on infrastructure and ecology

Golden mussels attach in dense colonies to hard surfaces. In other regions infestations have:

• Clogged intake pipes and reduced pump flow
• Fouled hydroelectric turbines and increased maintenance costs
• Altered food webs by filtering plankton, potentially favoring harmful algal blooms
• Threatened native mussels and other aquatic species

Practical risk: the same threats now face portions of the State Water Project that serve millions of Californians (background and context at Keep Tahoe Blue and the DWR release).

For recreation, dense colonies can coat docks, boat hulls and launch ramps with sharp growths that cut people and damage gear, increasing hazards and maintenance demands for popular sites.

Containment and response measures

Operational changes now in effect: Silverwood Lake (San Bernardino County) is classified as infested; managers have stopped routine entry inspections and moved to exit-only inspections with required vessel precautions, including removing drain plugs and following “clean, drain and dry” protocols. Pyramid Lake (Los Angeles County) also remains under exit inspection rules. Read the DWR release for operational guidance.

Lake Perris is at high risk because it receives daily transfers from Silverwood; agencies continue entry inspections there in an effort to keep it free. If Lake Perris tests positive, protocols would shift to an exit-only model to reduce spread.

“The recommended practice for boaters remains clean, drain and dry after every outing,” state officials emphasize, urging vigilance to prevent human-assisted spread.

Regulatory and legal steps

California placed the golden mussel on its restricted species list, effective Dec. 19, 2024, making import, transport or possession illegal. That legal status supports enforcement of boat inspection and decontamination rules (see the California Department of Fish and Wildlife notice).

Agencies including the Department of Water Resources (DWR) and California Department of Fish and Wildlife (CDFW) are coordinating monitoring, outreach, research and investments to protect infrastructure — stressing prevention because there is no effective means to eradicate the mussel from large water bodies at present.

Scope of the statewide threat

State officials report infestations now span more than 300 miles of waterways in California. That coverage raises the stakes for pumps, conveyance facilities and treatment systems that serve cities, farms and ecosystems — and means that connected channels, transfer systems and human activity could expand the mussel’s range if precautions lapse (background: Keep Tahoe Blue; official release: DWR).

Public reporting and resources

Officials ask the public to report suspected sightings promptly. Contact CDFW at (866) 440-9530 or invasives@wildlife.ca.gov, and consult state information pages provided by DWR and CDFW (DWR release; CDFW notice).

Implications for San Diego

Economic impact: San Diego depends on regional and imported water; increased maintenance or failures in statewide conveyance systems could raise operational costs and affect local rates and budgets. Marina and boatyard firms may face higher cleaning and protection costs if mussels spread.

Infrastructure vulnerability: California’s interconnected water system means upstream problems can affect downstream users. San Diego providers must track transfers, inspections and treatments closely and may need investments in monitoring and hardening intake structures.

Political and social effects: Local officials may push for stronger state coordination and funding. Boaters and shoreline businesses should expect new inspection and decontamination measures that could mean delays, added costs and temporary closures.

Practical actions for San Diego residents and agencies

• Check before you launch: Know and follow inspection rules; if you visit Silverwood, Pyramid or other infested waters assume your boat needs decontamination (DWR guidance).
• Practice clean, drain, dry: Remove drain plugs, clean visible material, and dry boats and gear thoroughly between uses to reduce risk.
• Stay informed: Follow updates from DWR and CDFW, and report sightings to CDFW at (866) 440-9530 or invasives@wildlife.ca.gov.
• Support local planning: Encourage agencies and elected officials to prioritize monitoring, infrastructure assessments and coordinated responses that protect local water reliability and costs.

For more information

Official and reporting resources:

• Department of Water Resources news release
• Reporting from KPBS
• California Department of Fish and Wildlife notice
• Background on regional risks (Keep Tahoe Blue)

If you suspect golden mussels or see unusual growths on boats or infrastructure, contact CDFW at (866) 440-9530 or invasives@wildlife.ca.gov.