In only two years, a non-native species of mussels first found in the Port of Stockton has spread so quickly and is causing so much damage in the Delta that the San Joaquin County Board of Supervisors has declared a local emergency amid the invaders.
“This is out of control in our Delta,” Supervisor Paul Canepa said in backing the emergency proclamation, which passed unanimously in a vote at Tuesday’s meeting.
This isn’t the first time mussels have invaded local waters. But the golden variety, believed to have arrived in Stockton on a ship from Asia, is deemed particular devilish compared to zebra and quagga mussels. While relatively tiny, the golden mussels can grow quickly into clusters that clog drainage pipes, dam gates and jam up boat plumbing.
First discovered in San Joaquin County in October 2024, the golden mussels have spread to waterways throughout California. State officials have required boat inspections at lakes and taken other steps to try to stem the spread, but the problem has continued.
A single golden mussel can produce up to 1 million offspring in a year, which explains their quick spread. It can take 10 hours and cost $10,000 to clean mussels off floodgates, according to county staff. If the gates aren’t cleaned, they can’t properly close, and then water can rush through and cause flooding.
Central Valley counties are already getting help from the state, which has declared its own emergency. Golden mussels have been added to a restricted species list.
Three bills are moving through the California Legislature. Besides having secured $20 million in initial funding to deal with the pesky bivalves, Assemblymember Rhodesia Ransom, D-Tracy, is urging state funding for decontamination centers in the Delta.
Supervisor Mario Gardea said now is the time to sound the alarm about the dangers the mussels pose.
He said he was able to see the damage on a visit to McDonald Island. There, mussels were coating intake and exhaust pipes needed to move water to keep the island from flooding. Plus, “it’s not just the pipes,” Gardea said; mussels had attached themselves to rocks and other structures.
The Board of Supervisors was told that boaters and farmers are taking some of their own countermeasures. Some boat owners are experimenting with ultrasonic systems that can help deter the mussels from attaching to their vessels. And some farmers are reportedly replacing irrigation pipes, rather than trying to clean them, when they become clogged with mussels.
Gardea said he believes the infestation is so pervasive that ridding the state of golden mussels is impossible.
Now, he said, “it’s about mitigation. We’re not going to be able to eradicate these mussels out of our system.”