Invasive mussel found in North America for first time, posing immediate threat in California’s Delta

A particularly worrisome mussel species has entered North America for the first time through the Sacramento-San Joaquin River Delta — sparking what many are calling an immediate threat to California’s most significant watersheds.

Golden mussels, invasive freshwater bivalves that have devastated ecosystems and critical water infrastructure in other parts of the world, were recently discovered near the Port of Stockton. Limnoperna fortunei appear to have also found their way many miles downstream into O’Neill Forebay of the San Luis Reservoir, where officials in Merced County have been rapidly conducting genetic testing.

“The species poses a significant immediate threat to the ecological health of the Delta and all waters of the state, water conveyance systems, infrastructure and water quality,” according to a public alert by the California Department of Water Resources and the California Department of Fish and Wildlife. “This discovery is the first known occurrence of golden mussels in North America.”

These mussels probably infiltrated California by a ship traveling from an international port and are likely to spread throughout the Delta and through the water infrastructure associated with the Delta, officials said in a statement. “Without containment, golden mussels are likely to spread to other freshwater bodies in California, and to other ports and inland waters of North America, and abroad.”

These tiny dark-yellowish mollusks, native to rivers in China and Southeast Asia, have already wreaked havoc in South America, and for years have kept officials and ecologists across the United States on high alert. In each country where the mussels have taken over, the initial introduction also appeared to be from ships — on the hulls or from ballast water release.

And in most of these cases elsewhere, the golden mussel’s range rapidly expanded up or downstream from the point of introduction — usually at a port and then through local, human-mediated pathways, officials said.

Both a freshwater and brackish species, the golden mussel can tolerate wide ranges in salinity, temperature and pH levels, and cantravel much farther than people might think. Shortly after fertilization, the larvae become mobile and are capable of coordinated swimming as they disperse in the water column.

Golden mussel takeovers in other countries have shown that the species can grow in clumps or colonies containing as many as 80,000 to 200,000 organisms per square meter.

Wildlife officials have noted that the golden mussel can survive in considerably lower-calcium waters than either the quagga or zebra mussel, which have caused quite a few problems across lakes and reservoirs in California, as well as in the Great Lakes region and in many other lakes across the United States.

In addition to disrupting the ecological balance of an entire fresh body of water, golden mussels pose a significant threat to California’s water infrastructure. These mussels can clog critical water intakes and fish screens and also foul major pipes relied on for water supply.

Agricultural irrigation and power plant operations could also be significantly impeded, and if past mussel infestations are any indication, golden mussels could also severely affect boating and recreation by encrusting docks, engines and steering equipment.

In California, a team of state, local and federal agencies has been actively monitoring and coordinating the next steps to contain the species from spreading further in California and beyond. Officials have called upon anyone working and recreating in California lakes and rivers to clean, drain and dry their watercraft and equipment every time they are removed from a body of water. (The California State Parks’ Division of Boating and Waterways has a webpage detailing how to “clean, drain and dry” a boat.)

“This simple measure has served to prevent spreading quagga and zebra mussels and is equally effective in stopping the overland spread of golden mussels,” officials said.

Those who observe any suspected golden mussels in California are asked to file a report through CDFW’s Invasive Species Program, either by filling out the form online, emailing invasives@wildlife.ca.gov or calling (866) 440-9530. Please note that officials are asking for these citizen reports to include the specific location of the observation and at least one clear close-up photograph of the mussel.