Golden mussels in California: What Santa Clara County needs to know

April 3, 2026

Banner showing a reservoir at sunset with the headline “Protect Our Reservoirs.” It warns that golden mussels threaten local recreation and urges boaters and anglers to “Clean. Drain. Dry.” Icons show prohibited wet live bait (fish, crayfish, mussels) and steps to stop the spread: remove plants, drain water, and wipe down equipment. Footer includes ValleyWater.org/GoldenMussels and logos for Santa Clara County Parks and Valley Water.

California’s water infrastructure is facing a new threat—one that’s tiny, invasive, and alarmingly fast-spreading. Golden mussels, native to Asia, were first detected in the Delta in 2024 and have spread to several California waterbodies hydrologically connected to the Sacramento-San Joaquin Delta, including San Luis Reservoir. These invaders pose a serious risk to water delivery systems across the state, including those serving Santa Clara County.

Why golden mussels are a threat

Golden mussels threaten native ecosystems and water infrastructure by growing in dense layers that clog pipes, pumps, and other equipment. They spread by attaching to boats, plants, and recreational gear, often moving from infested waters to clean ones. Their microscopic larvae can also be transported in live wells, bilges, or bait buckets, making them difficult to control.

Santa Clara County reservoirs: Still mussel-free

The good news? Golden mussels have not been detected in any of Valley Water reservoirs in Santa Clara County.

But prevention is key. Once golden mussels take hold, the cost of containment and infrastructure damage can soar into the millions.

To learn more about golden mussels, visit valleywater.org/goldenmussels.

How you can help

All boats entering Valley Water reservoirs must be inspected to prevent infestation. This is part of a partnership between Valley Water and Santa Clara County Parks.

Santa Clara County residents play a vital role in keeping our reservoirs safe. Here’s what you can do:

Boaters: Always follow the “Clean, Drain, and Dry” protocol before entering or leaving any water body.
Anglers: Do not use wet live bait. Avoid transferring bait or water to another water body.
Report sightings: If you suspect golden mussels, contact the California Department of Fish and Wildlife at [email protected] or online.
Stay informed: Check inspection requirements before visiting local lakes and reservoirs.

For information about boating inspections, rules, park hours, and launch reservations, visit the Santa Clara County Parks website.

Valley Water manages an integrated water resources system that includes the supply of clean, safe water, flood protection and stewardship of streams on behalf of Santa Clara County's 2 million residents. Valley Water effectively manages 10 dams and surface water reservoirs, three water treatment plants, an advanced recycled water purification center, a state-of-the-art water quality laboratory, nearly 285 acres of groundwater recharge ponds and 333 miles of waterways. We provide wholesale water and groundwater management services to local municipalities and private water retailers who deliver drinking water directly to homes and businesses in Santa Clara County.