SAN DIEGO -- A shark was sighted at San Onofre state beach Saturday morning, 10News reported.

An experienced surfer told lifeguards he saw a white shark come up next to him. The shark bumped him hard enough to turn his surfboard around.

No sharks have been sighted since. But surfers who know the area say they have seen them there in the past.

John Fontana, a surfer, said, "You think they're dolphins until you get close and you realize it's not a dolphin -- it's a shark. You paddle quickly but quietly to the shore."

Lifeguards are not keeping people out of the water but are warning them to be on the lookout.