Tuesday, 28 July 2026, 12:17
The Yolo County Board of Supervisors unanimously proclaimed a local emergency on Tuesday, July 21, 2026, in response to the invasion of golden mussels (Limnoperna fortunei) in waterways connected to the Sacramento-San Joaquin Delta. The declaration follows requests from the West Sacramento city manager and the Port of West Sacramento director, and aligns with similar actions by Sacramento, San Joaquin, and Kern counties, as well as the city of Stockton. The resolution allows the county to formally request money from the state to assist in mitigation and control, and no fiscal effect is expected, according to a report from county administrators. Ratification of the declaration will support the county’s ability to seek state and federal assistance with associated costs.
“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 Chair of the Yolo County Board of Supervisors Sheila Allen. “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.”
“Our hope is that by declaring an emergency in response to this, that we can access funding and other resources that may be available to address this invasive species,” said Will Arnold, a Yolo County spokesperson.
West Sacramento Mayor Martha Guerrero is calling for immediate action to remove the mussels. “We need to get that immediately here in West Sacramento, in partnership with the reclamation district, to make sure those discharge pipes are clear,” she said. She hopes for the state to send resources soon, given that the longer the mussels spread, the more expensive it will become to remove them from water infrastructure.
The first North American detection of golden mussels occurred in October 2024 when shells were collected at a water quality station at Rough and Ready Island near the Port of Stockton. The mussels were first discovered in the Port of Stockton itself in November 2024. Since then, the mussels have rapidly colonized Delta waterways. On June 27, 2026, the California Department of Fish and Wildlife confirmed their presence in Yolo County waters at the Port of West Sacramento. The mussels reproduce prolifically, attach to nearly any submerged surface, and form dense colonies that clog water intakes, pipes, pumps, and conveyance systems while displacing native species. In the Delta, they compete with native species like juvenile salmon for food, disrupting the ecosystem. The invasive species also outcompetes crawfish, which decreases the food source for fish and other wildlife.
West Sacramento Mayor Martha Guerrero highlighted immediate risks: “Say there's heavy rain. We have to get the water out of the city. We live in a bowl. My concern is, the only way to be able to do that is by sending divers in.” “They go into pipes and drains in areas where we are required to either bring in water or to pump water out,” Guerrero added. The mussels have already infested drainage pipes and pump stations, threatening flooding during storms. Some researchers also link golden mussels to toxic algal blooms.
The invasion affects the entire Sacramento-San Joaquin Delta, a critical water hub for California. Yolo County’s declaration supports a coordinated regional response, as Supervisor Oscar Villegas noted: “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.” Reclamation District 900, which manages West Sacramento’s drainage, is working with port leaders to clear discharge pipes. The mussel population in the Port of West Sacramento is believed to have stemmed from a source population within the vicinity, according to a statement from the Department of Fish and Wildlife.
Sacramento County declared a local emergency for the mussels in June 2026, and San Joaquin County declared a local emergency in April 2026, having launched a task force in October 2025 to stop the spread. Stockton also has its own local emergency declaration.
Golden mussels, native to Southeast Asia, have invaded South America and are now established in California. The state Department of Water Resources detected the golden mussel in the Delta in 2024, marking the first sighting in North America. Following the initial discovery, mussels were observed at numerous other locations throughout the Delta. State experts say eradication in open waters like the Delta is unlikely, so efforts focus on slowing spread, protecting infrastructure, and monitoring. The species can hitchhike on boats, trailers, and gear, and its microscopic larvae are invisible, making prevention critical.
The state took a harsh stance towards the uninvited mollusks right away, investing $6 million to combat their spread in late June after state officials became worried that their presence would increase maintenance costs and harm the state’s water supply. The Sacramento-San Joaquin Delta supplies fresh water to two-thirds of the state’s population and millions of acres of farmland, according to the California Department of Water Resources.
Residents and boaters can help by following the Clean, Drain, Dry protocol: clean equipment, drain all water, and dry for at least five days before entering new waters. Report sightings to the California Department of Fish and Wildlife via their online form, email [email protected], or call 866-440-9530.
For more information on how to prevent the spread of invasive aquatic species, visit stopaquatichitchhikers.org.
