Over a three-day span this week, the Marine Mammal Center in Sausalito says they rescued 15 to 20 sick sea lions and they expect that number to grow.
Many are having seizures, disorientation, and abnormal behavior.
So far, there's no answer to why cases are going up, but beachgoers are being warned to keep an eye out.
"They are not their normal selves. Wild animals are already unpredictable and especially so when they have an algal toxin that's impacting both their memory and cognitive portion of how they behave, but also increases potentially unpredictable behavior," said Giancarlo Rulli, of the Marine Mammal Center.
At least three sea lions were found dead in Monterey County.
The Marine Mammal Center is urging the public to contact them if they encounter a sea lion in distress, rather than approaching the animal themselves.