Golden mussels pose a significant threat because of their rapid reproduction, ability to attach to nearly any submerged hard surface, and high-capacity filter feeding. Photo designed by Magnific

WOODLAND, CA (MPG) - The Yolo County Board of Supervisors has proclaimed a local emergency in response to the spread of invasive golden mussels in waterways connected to the Sacramento-San Joaquin Delta.

The proclamation strengthens Yolo County’s ability to coordinate with local, regional, state and federal partners, pursue funding and technical assistance, and support long-term efforts to protect water infrastructure, agricultural water deliveries, flood-control facilities, native ecosystems and the regional economy.

“Golden mussels pose a serious long-term threat to the water systems and natural resources that support communities across Yolo County and the Delta region,” said Sheila Allen, chair of the Yolo County Board of Supervisors. “This proclamation gives the County a stronger footing to work with our partners and seek the resources needed to protect public infrastructure, agriculture and the environment.”

On June 25, the California Department of Fish and Wildlife notified Yolo County and local partners of confirmed golden mussel detections in county waterways connected to the Sacramento-San Joaquin Delta. First discovered in San Joaquin County in October 2024, the invasive freshwater species has since spread through parts of the Delta and collected water-conveyance systems.

The emergency proclamation follows coordination with the City of West Sacramento and the Sacramento-Yolo Port District, both of which have identified growing risks posed by the infestation. Yolo County joins neighboring jurisdictions including Sacramento County, San Joaquin County and the City of Stockton, which have already declared local emergencies in response to the same regional threat.

“This issue is especially important for West Sacramento and the communities that depend on the Delta’s connected waterways,” said Oscar Villegas, Yolo County Supervisor for District 1. “Golden mussels do not stop at city, county or agency boundaries. We need a coordinated regional response that helps protect water reliability, flood-control systems, agriculture and local infrastructure.”

“The City of West Sacramento is committed to working with Yolo County, the Sacramento-Yolo Port District, state agencies, and regional partners to help slow the spread of golden mussels and protect shared waterways and infrastructure,” said Martha Guerrero, mayor of West Sacramento. “This partnership will help us provide clearer guidance to residents and visitors as this issue continues to develop.”

Golden mussels pose a significant threat because of their rapid reproduction, ability to attach to nearly any submerged hard surface, and high-capacity filter feeding. They readily colonize rocks, docks, water intake structures, pipes, pumps, irrigation infrastructure, boats and other submerged equipment. Dense colonies can clog water intakes, pipes, pumps, watercraft engines and other water-conveyance systems.

Infestations can significantly increase operations and maintenance costs, reduce the efficiency of water delivery systems, interfere with flood control and hydropower facilities, and damage recreational watercraft.

In the Sacramento-San Joaquin Delta, golden mussels also compete with native species, including juvenile salmon, for food by filtering tiny plants and animals from the water. This can disrupt the natural food chain, degrade habitat, and threaten the health of the Delta ecosystem, creating lasting environmental and economic impacts.

Golden mussels spread through the movement of boats, trailers, anchors, fishing gear, pumps and other equipment that have been in infested waterways. Their microscopic larvae can be transported in standing water found in bilges, ballast tanks, live wells, bait buckets, engine cooling systems and other compartments. Juvenile and adult mussels can also attach to submerged surfaces and hitchhike to new waterways. 

Because the larvae are invisible to the naked eye, golden mussels can spread unknowingly if watercraft and equipment are not properly cleaned, drained and dried.

State agencies and invasive species experts have determined that eradication from open waters such as the Sacramento-San Joaquin Delta is not likely to be feasible once golden mussels are established. As a result, response efforts are focused on slowing the spread of the invasive species, protecting critical infrastructure, supporting early detection and monitoring, and minimizing impacts to California’s water systems, agriculture, fisheries, recreation and natural resources.

Residents, anglers and recreational boaters can play a critical role in preventing the spread of invasive mussels by following the Clean, Drain, Dry protocol.

Before leaving any boat launch or water access site: clean off all visible aquatic plants, animals and mud from boats, trailers, anchors, fishing gear and other equipment; drain all water from bilges, live wells, motors, ballast tanks, bait buckets and any other water-containing devices; and dry all equipment completely for at least five days before launching into another waterbody.

Anglers should also remember to dispose of unwanted bait, worms and fish parts in the trash. If keeping live bait, drain bait containers and refill them with spring water or dechlorinated tap water. Never release live fish, bait or other aquatic organisms from one waterbody into another.

For more information about how to help prevent the spread of aquatic invasive species, visit stopaquatichitchhikers.org.

For more information on where current infestations of Golden mussels have been detected, visit the California Department of Fish and Wildlife's invasive species resources.