LOS ANGELES >> A 20-year-old man died after lightning from a rare summer thunderstorm jolted a Southern California beach, injuring or rattling more than a dozen people, authorities said.

Witnesses said they saw a glare of light and heard a tremendous boom as lightning struck the water off of Venice Beach around 2:30 p.m. Sunday. Swimmers cooling off on a muggy day, volleyball players on the sand and people strolling the famous boardwalk were jolted.

A 20-year-old man was taken from the beach to a hospital where he died, Los Angeles County coroner’s Lt. Larry Dietz said. His identity was not immediately released.

Confirmation of the cause of death was pending an autopsy. Dietz said he also can’t confirm whether the man was a swimmer who was pulled from the water and given CPR.

Twelve other people, including a 15-year-old boy, were examined after they felt the effects of the lightning, ranging from anxiety to a man who needed cardiopulmonary resuscitation. However, not all were necessarily actually struck by lightning, said Katherine Main, a city fire spokeswoman.

Nine were taken to hospitals, where one was listed in critical condition.

Most of the others were mainly shaken up and expected to recover, fire officials said.

Lightning also struck a 57-year-old man on a golf course on Santa Catalina Island. He’s in stable condition

Stuart Acher said he was shocked while playing volleyball on the beach.

"We went about our game and then all of a sudden, there was a big flash of light and a boom, and it felt like someone punched me in the back of my head," he told KABC-TV. "It went down my whole side of my right body, and my calves sort of locked up, and I fell over. And I looked up and everybody else was, you know, falling over."

Paramedics examined Acher but he felt all right and went back to playing volleyball.

Steve Christensen said his friend had been body-surfing and was sitting on the beach when lifeguards began searching for a missing swimmer.

"He (Christensen’s friend) went out to the water to find him and walked right into him," Christensen said. "He was face down on the bottom."

Christensen said his friend pulled the man, who appeared to be in his 20s, from the water, and lifeguards began CPR before taking him away.

"The guy wasn’t moving. He wasn’t responding at all," Jesus Zamudio of Riverside told the Los Angeles Times (http://lat.ms/UvUQgs ).

"This tragedy reminds us that we can take nothing for granted or underestimate the power of nature," Mayor Eric Garcetti said in a statement.

Earlier, off the coast, lightning struck a 57-year-old man on a golf course on Santa Catalina Island but he was taken to a hospital in stable condition, said Steve Denning, a law enforcement technician with the Los Angeles County Sheriff’s Department. He did not have other details.

The lightning strikes occurred as a fierce but brief thunderstorm hit the island, dumping more than three-quarters of an inch of rain in about two hours, causing minor flooding and setting two small fires in the brushy backcountry that were quickly doused.

Hundreds of lightning strikes were reported all around Southern California as a moisture-laden monsoonal flow spread up from the south and swept the region all the way out to the ocean.

"This is pretty rare" because usually the flow affects just the deserts and sometimes the mountains, said Stuart Seto, a weather specialist with the National Weather Service in Oxnard.

The storms began to dissipate as they moved northwest, leaving just a chance of storms through Monday, mainly in the deserts and mountains, Seto said.