Invasive golden mussels have spoiled boating season on the Sacramento-San-Joaquin Delta after East Bay Municipal Utility District announced in April the closure of boat launches in 2025 while the public utility studies the prevention and removal of the mollusks.
EBMUD seeks to prevent one of the most common ways that golden mussels spread — in water held on vessels that is then expelled in other waterways –because if the mussels cross into EBMUD’s infrastructure, they could clog pipes, pumps, and lead to costly removals. If EBMUD’s efforts should fail to contain golden mussels, the little pests could become a big problem for the water agency and the delta ecosystem, EBMUD biologist Paul Gilbert-Snyder said.
“There is no known way to remove them, short of things like drawing down a reservoir and then maybe chemically treating the very bottom of the reservoir,” Gilbert-Snyder said. “Once you have them, you pretty much have them.”
EBMUD is the public water utility for 1.4 million customers in the East Bay. The organization sources water from the 578-square-mile watershed of the Mokelumne River on the western slope of the Sierra Nevada, which feeds into the Sacramento-San Joaquin Delta.
Golden mussels were found for the first time in the Sacramento-San Joaquin Delta in October of last year, marking the first time they had been recorded in North America. Originally from Southeast Asia, the invasive filter-feeder has been found in Hong Kong, Japan, and Taiwan since the late 1960s, according to the U.S. Geological Survey. More recently, they have spread to South American countries like Paraguay, Argentina, and Brazil, where they pose a risk to the Amazon, alarming researchers about the speed of their worldwide invasion.
Biologists at EDMUD are concerned about containing golden mussels — the first invasive mussel found in Northern California — because they are far more adaptable than other invasive species in California’s waterways, able to survive in habitats with less calcium and higher water temperatures than other invasive species like quagga mussels, according to Gilbert-Snyder. Mitigation efforts for quagga mussels by the Metropolitan Water District of Southern California have cost millions of dollars, but golden mussels pose an even more serious threat.
“When they’re first born, their larval stage is microscopic, so they can move wherever the water is moving. They can settle on the inside of your pipes, on your screens… and then they start growing layer upon layer,” Gilbert-Snyder said. “That’s why there’s so much effort that goes into prevention.”
Adult golden mussels range in size from 1/2 to 2 inches. Once biologically mature at the age of three months, an adult female golden mussel can produce up to one million eggs per year. Though the Department of Fish and Wildlife identified the first golden mussel in the Sacramento-San Joaquin Delta in October 2024, Gilbert-Snyder estimates many thousands there today.
The ban on private boating will affect mariners at each of EBMUD’s reservoirs, including Pardee Reservoir, the Camanche Reservoir North and South in the Sierra Foothills and San Pablo Reservoir in the East Bay, according to EBMUD. A 2009 risk analysis by the agency determined that all of EBMUD’s reservoirs were “vulnerable to decontamination protocols” from golden mussels, so the public utility is being conservative about the freedom of boaters until the threat is fully determined.
“Although boat quarantines and decontamination stations can help reduce the likelihood of introduction, risk remains,” an April EBMUD announcement states. “EBMUD is working closely with state and federal agencies, research institutions, and other water managers to track the spread, monitor boat traffic, test inspection practices and decontamination protocols, and prepare long-term plans in the event the mussel is introduced into the reservoirs.”