Napa supervisors signal intent to adopt ordinance to inspect boats for invasive mussels at Lake Berryessa

The Napa County Board of Supervisors on June 24 signaled its intent to adopt an ordinance authorizing inspections of watercraft at Lake Berryessa to prevent the spread of invasive golden mussels.

The effort follows a technical presentation by Martin Peralez, a PhD aquatic ecologist with the Napa County Resource Conservation District, who told the board the golden mussel has been newly detected in California's Sacramento–San Joaquin Delta and poses both ecological and infrastructure risks. "These mussels are relatively small. They're in the inch to inch and a half range," Peralez said, adding that researchers detected the species in the Delta "near Stockton at Ruffin Ready Island." He warned the mussels reproduce quickly, can spread as attached adults or as microscopic free‑swimming larvae called veligers, and can survive out of water for weeks.

The ordinance would add a chapter to the county code (chapter 6.02) authorizing county inspectors, concession staff and law enforcement to stop and inspect boats, trailers and other watercraft entering Lake Berryessa, improve tag and decontamination tracking and create enforcement tools including fines and a misdemeanor for deliberately avoiding inspections.

Why it matters: Golden mussels and related invasive freshwater mussels can clog intake pipes and infrastructure, alter food webs and water quality in reservoirs, and foul shoreline areas with sharp shells. Peralez told the board that once established, eradication is effectively impossible and that prevention is the most cost‑effective approach.

Key facts and county discussion - Detection and risk: Peralez said the golden mussel is native to East Asia, arrived in South America in the 1990s and was first detected in the Delta in October (as presented). He described how females can produce hundreds of thousands to a million eggs and that veligers are microscopic and easily moved in small amounts of water. - How inspections work: County counsel explained the existing inspection program at Lake Berryessa is already being implemented administratively in cooperation with the U.S. Bureau of Reclamation and the Solano County Water Agency; the ordinance would codify that program and extend inspection authority to cover non‑trailered craft such as canoes and other gear. "When a boat is tagged, it is because it's either been decontaminated ... or you can just leave it outside for at least 30 days," county counsel said, describing the tag and quarantine approach used to ensure vessels are not moving live mussels between water bodies. - Tagging and decontamination: Counsel described a tag placed between a boat and trailer that must be broken to launch; a boat leaving an invaded area and then arriving at Berryessa without a valid tag will be denied launch. Staff said decontamination typically involves hot water under pressure and can take roughly an hour, or a boat can be dried and held for 30 days. - Enforcement and penalties: The draft ordinance includes misdemeanor language for anyone who attempts to evade inspection with specific intent. The sheriff's representative told supervisors the ordinance uses a "may inspect" standard to give deputies flexibility, but that the ordinance will provide teeth for enforcement where prior practice lacked penalty authority. - Resource and implementation questions: Board members asked about inspection staffing, signage and public education. The sheriff and staff said the county will continue to work with concessionaires and Solano County Water Agency; concession operators and some federal sites already screen boats. The sheriff warned enforcement may require additional resource commitments by the county in some cases and suggested concessionaires could provide more decontamination capacity.

Action taken The board voted unanimously to express intent to adopt the ordinance (motion by Supervisor John Manfry; second by Supervisor Peggy Alessio). The action does not finalize the ordinance but sets the process to return for formal adoption following required public hearings.

What remains Staff told the board the ordinance will return for the formal adoption process and that the county will continue coordination with the Solano County Water Agency, Bureau of Reclamation and concession operators on signage, public outreach and staffing details. Board members asked staff to pursue clearer cost‑sharing or reimbursement arrangements with Solano County Water Agency for inspection and enforcement workload.

The county presentation and the briefing emphasized prevention, early detection (plankton/veliger monitoring and eDNA were noted as detection tools) and public outreach as the primary means to avoid long‑term damage to infrastructure and recreation at Lake Berryessa.

Ending note: Supervisors said they want the public to understand the risk and the reasons for inspections, and staff pledged to expand outreach and post clear requirements at launches and access points.