At Seal Beach, 45 km southeast of downtown Los Angeles, researcher Chris Lowe and his team caught dozens measuring and tagging them before release. Lowe estimates that more than 16,000 stingrays can gather in an area the size of a football field in a single day. The species has concentrated at the site for at least 60 years, helped by warm water discharged from a nearby power plant and fine sediments that provide suitable habitat.

The increase is also being felt by swimmers. Two state beaches near Huntington Beach have recorded more than 3,100 sting incidents so far in 2026, about twice the total for all of 2025. According to Chris Lowe, Southern California has the highest number of stingray injuries, largely because round stingrays bury themselves in the sand and may strike when people step on them. He expects incidents to increase as El Niño warms coastal waters and brings more subtropical rays north from Baja California.

National Oceanic and Atmospheric Administration says a marine heatwave has already persisted off parts of the US West Coast for an unusually long period.