Invasive golden mussels found in Alameda County's Lake Del Valle prompt 30-day boat quarantine

A species of highly invasive mussel have been found at an Alameda County lake, prompting authorities to issue a quarantine on boats that launch at the lake.

The East Bay Regional Park District said on Monday that golden mussels were detected at Lake Del Valle in Del Valle Regional Park southeast of Livermore. The mussels are native to coastal Asia and parts of South America, similar to the invasive quagga and zebra mussels but able to thrive in water with lower calcium levels, which put local water sources and ecosystems at greater risk of invasion, the district said.

The district said that effective immediately, boaters launching at Lake Del Valle are subject to a 30-day quarantine before their watercraft will be permitted at any other waterbody managed by the district. 

"Boats that launch exclusively at Lake Del Valle and return with an intact Del Valle boat band will not be subject to the quarantine, said a press release from the park district. "Other agencies that manage waterbodies elsewhere in the Bay Area and beyond may impose their own quarantine requirements, so boaters should check the websites of respective managing agencies for current rules."

Golden mussels were first detected at the Port of Stockton in 2024, the first known occurrence of golden mussels in North America, the district said. The mussels were believed to have been introduced by a ship traveling from an international port, according to the California Department of Fish and Wildlife.

Since then, their proliferation has led to the closure of California reservoirs and local emergency declarations in San Joaquin and Yolo counties. Before the discovery at Lake Del Valle, Contra Loma Reservoir in Antioch was the only other East Bay Park District waterbody where golden mussels had been detected, and boaters at Contra Loma are now under the same quarantine rules being implemented at Lake Del Valle.

Boats without an East Bay Park District boat band are subject to inspection for the presence of golden, quagga and zebra mussels. Inspection is required for boats, kayaks, canoes, sailboats, inflatable craft, and any type of floating board, the district said.  The mussels can attach to nearly any underwater surface, including boats, ropes, buoys and aquatic plants that become entangled on anchors and trailers.

Inspections are currently required at:

• Contra Loma Regional Park
• Del Valle Regional Park
• Lake Chabot Regional Park
• Quarry Lakes Regional Recreation Area
• Shadow Cliffs Regional Recreation Area