Napa supervisors signal intent to authorize boat inspections at Lake Berryessa to keep invasive mussels out

The Napa County Board of Supervisors on Tuesday voted unanimously to express its intent to adopt an ordinance that would add chapter 6.02 to the Napa County code authorizing inspections of watercraft for invasive mussels at Lake Berryessa.

County counsel Tom Zalley opened the public hearing by framing the action as a preventative measure: “Lake Berryessa is clean right now. We don't want those mussels in there,” he told the board before turning the presentation over to county and conservation staff.

The board's action follows a presentation from Martin Peralez, a PhD aquatic ecologist with the Napa County Resource Conservation District, who described the golden mussel as a highly invasive freshwater species recently detected in California's Delta. Peralez warned the species is prolific and mobile: “They can survive out of water for weeks,” he said, and described both adult mussel fouling of hulls and microscopic free‑swimming larvae — known as veligers — that can travel inside bilges, live wells and water on boats.

Why it matters: Peralez and county counsel described two categories of risk. Ecologically, mussels can alter food webs, outcompete native species and worsen harmful algal blooms. Economically and for infrastructure, they can clog intake pipes, line the inside of conduits and foul launch infrastructure — creating prolonged, costly maintenance and potential shutdowns of water delivery systems and recreational facilities.

County staff said an inspection and tagging program is already in use administratively at Lake Berryessa through cooperative efforts with the U.S. Bureau of Reclamation and the Solano County Water Agency; the ordinance would codify and slightly expand that program. Under the current operational protocol, boats that have been decontaminated are fitted with an identifiable cable tag that must remain in place until the vessel leaves a launch. Decontamination typically involves hot‑water pressure washing that can take about an hour; an alternative is a quarantine period of at least 30 days, staff said.

Sheriff's Office staff briefed the board on enforcement mechanics and resource implications. The ordinance uses “may inspect” language for deputies rather than a mandatory duty, which the sheriff said provides operational flexibility but also gives deputies authority to issue citations where violations occur. County counsel said the proposed code would make launching a motorized boat in Lake Berryessa without a valid tag an infraction and would establish a misdemeanor for deliberate attempts to avoid inspection.

Board members pressed on monitoring and regional implications. Supervisor Manfry asked about risks to state water project intakes and the North Bay Aqueduct; Peralez said the species' spread through conveyance infrastructure already has managers concerned and that monitoring using plankton nets and eDNA is being employed elsewhere to detect veligers early. County counsel clarified that Lake Berryessa inspections are a joint operational program already run with concessionaires, the Bureau of Reclamation and the Solano County Water Agency, and that codifying authority would let deputies and authorized staff inspect non‑trailered craft such as canoes or kayaks for signs of fouling as well as motorized boats.

Motion and next steps: Supervisor Manfry moved, Supervisor Alessio seconded and the board voted unanimously to express its intent to adopt the ordinance; staff said the formal adoption will return at future hearings after the required public meetings. County counsel and resource district staff said they will continue outreach and signage at freeway exits and launches, and staff indicated selected boats will continue to be inspected and decontaminated under the existing program while the ordinance moves through its remaining public‑notice steps.

The board and staff framed the action as precautionary rather than punitive: council and conservation staff repeatedly emphasized prevention and coordinated monitoring as the most cost‑effective approach given there is no feasible large‑scale eradication once a population becomes established.

A formal ordinance adopting chapter 6.02 and an implementation plan will return to the board for adoption after the required follow‑up hearings and notice periods, county staff said.