Ambulances were called to La Jolla Wednesday afternoon after at least 30 people were stung by stingrays.
The attacks happened at both La Jolla Shores and Blacks Beach up the coast to the north.
Lifeguards said that at one point, they were treating 11 or 12 people at the same time.
Paramedics were called in to assist with triage because of the abundance of victims. Most of the victims are treated by immersing the stung spot in hot water right away. However, they monitored the victims' vital signs.
A lifeguard said that if you are allergic to bees, it's likely that you are allergic to stingrays, too. Two people were taken to the hospital for their injuries.
Police said that while such a high number of victims in one day is unusual, it is not unheard of.
"We've really had a large amount of folks affected today, so I would say it's not normal," said Lifeguard Sgt. John Sandmeyer.
Sandmeyer said it was atypical to have so many people stung at the same time.
Tuesday may have offered lifeguards at La Jolla Shores a hint of things to come, when more than 20 people were stung.
"We are seeing a lot of folks out there needing to shuffle their feet a little bit better," Sandmeyer said.
Lifeguards urge swimmers to shuffle their feet when entering and exiting the water to avoid stingrays.
Stingrays are not the only sea creatures being detected in large numbers.
Large jellyfish are popping up along San Diego’s shoreline this week. Scientists say a rare species of dark purple jellyfish called the black sea nettle is showing up in San Diego Bay and washing ashore on beaches.