Santa Clarita / Antelope Valley : L. A. Man Drowns During Castaic Lake Outing : Accident: Victim, who died during rescue of two youths, was part of group swimming in area closed to public, officials say.

A Los Angeles man who apparently didn’t know how to swim drowned Monday at Castaic Lake while helping rescue two children, authorities said.

The 20-year-old man, whose name was withheld pending notification of his family, was part of a group that sneaked into a roped-off area that is off limits to the public, officials said. The area cannot be seen by lifeguards at a nearby boat launch ramp, officials said.

Members of the group were using a piece of floating foam, which they apparently found on shore, as a makeshift raft. The foam is typically used to help support boat docks, said Peter Moore, a senior lifeguard at the lake.

“There were seven of them on this little float out there,” Moore said. “It’s marked ‘No Trespassing’ and ‘No Swimming’ all over.”

Two children in the group, ages 7 and 8, fell off the raft in water about six feet deep, and two of the adults went after them and put them back on the raft, Moore said.

But one man was unable to make it back aboard the raft, said Sheila Ortega, a spokeswoman for the county Parks and Recreation Department.

“Our assumption is that he was not a good swimmer,” she said.

A fisherman ran about a quarter-mile to the lifeguard building to notify them that one of the rescuers had failed to surface, Moore said.

Lifeguard Towner Douglas said he and other lifeguards with diving equipment arrived about three minutes later. Those on the raft with the victim pointed frantically to the area he was last seen, indicating he had been underwater for about 15 minutes.

“[On] the second dive, I found he was at the bottom just laying there,” Douglas said.

Douglas and two other lifeguards performed cardiopulmonary resuscitation on the drowned man until paramedics arrived, but he never regained consciousness.

The victim was flown by helicopter to Henry Mayo Newhall Memorial Hospital in Valencia, where he was pronounced dead on arrival, officials said.

Regional Park Superintendent Frank Gonzales said the drowning occurred in an area located next to a dam that separates the upper and lower portions of the lake and is used to store excess water. He said the overflow area is owned by the state, so county lifeguards are not assigned to it.

The rafters apparently sneaked into the area using a steep rocky hill above the shoreline, Gonzales said. A small ridge separates the area from the boat ramp where a lifeguard is stationed, making it difficult to spot trespassers.

“I think they probably said, ‘Oh, man! We’ve got a spot nobody knows about,’ ” he said.