A leptospirosis outbreak is killing sea lions earlier in the season than normal.

The Marin County-based Marine Mammal Center serves a 600-mile stretch of California coastline, including the Monterey Bay. The nonprofit left its longtime Moss Landing location at the end of 2024 and moved into a new site in an industrial park in Castroville that accepted its first animal on June 1.

“The timing could not be better,” says spokesperson Giancarlo Rulli. “There’s a real need right now.”

That’s because of a leptospirosis outbreak. In July alone, the Castroville facility accepted 75 animals, mostly sea lions with leptospirosis.

“This is the hot zone,” Rulli says, referring to the Monterey and San Francisco bays. The outbreak began in early July in San Luis Obispo County and has been moving north. The bacterial infection had been largely unseen in the region from 2012-17, when ocean temperatures ran warmer than usual. Since then, it’s been constant. “From 2018 on, we have seen leptospirosis [outbreaks] every single year. That’s a concern,” Rulli says.

The bacterial infection is zoonotic, meaning it can spread between species through bodily fluids, primarily urine. For that reason, Rulli emphasizes it’s important for dog owners to keep their pets leashed so they do not approach live or recently dead animals at the beach.

About two-thirds of the animals rescued by the Center’s army of volunteers will die or be euthanized due to organ failure. On Aug. 26, a group of volunteers guides Preaches, a sea lion found on a dock in Moss Landing on Aug. 25, into a crate to be transported to Sausalito for diagnosis and treatment. Afterward, volunteers grab three body bags – two sea lions and a dolphin – to load into the van.