The announcement warned swimmers and surfers to calmly exit the water Wednesday afternoon. A lifeguard got in the helicopter and saw a smaller 7-foot shark, then confirmed a 12-foot shark in the surfline at "Old Man's" surf break at San Onofre's surf beach.
Other footage shows shark fins breaking the water, with deeper animals harder to see.
Southern California's ocean waters are warming up and its coastline is teeming with marine life - including great white sharks.
Later in the day, another group of Great White sharks was spotted off the coast of long beach. He said the sharks are believed to be juvenile great whites.
Sightings are not uncommon along the coast, but attacks are rare.
But while it might seem like sharks are becoming a bigger threat, experts say the opposite scenario is closer to the truth.
Because juvenile sharks don't hunt larger marine mammals, they're much less likely to mistake a swimmer for their typical prey.
The water isn't now closed, they report, but signs are posted with a shark advisory, and the earliest it will be lifted is Saturday morning.
No one was hurt, and OC Lifeguards Chief Jason Young said the situation wasn't dire enough to call for an ocean closure, which only occurs when the sharks are more than 8 feet long or acting aggressively. The shark bit her on the right buttock and upper leg to the bone.
Evans asked the crew, "What was the response of the people in the water?"
"We'd spot them periodically and toward the end of the summer, they disappeared", he said.
"We should also not see the sharks' presence as a threat or inconvenience", he added.