The triathlon starts off with a half-mile ocean swim. Participants fight the waves and battle each other to get past the breakers and out into open water.
Participants then shed their wetsuits and jump on their bikes, pedaling for 18 miles. The last leg is the 4-mile run, and for many, it is the most difficult part of the triathlon.
"I tell myself I don't feel the pain. I just keep going, keep going. That's all I keep doing," said triathlon participant James Burke.
ABC7's Phillip Palmer was a participant. He finished fifth in the celebratory division.
But the finish line isn't the only thing these athletes are moving toward.
"I went to the triathlon kickoff, and I saw this little boy Victor that talked about fighting cancer, and I thought what a great cause," said participant Colette Vanmierlo. "I was in shape; I was a runner, and I thought why not do this and help Children's Hospital?"
Proceeds from Sunday's triathlon will benefit Children's Hospital Los Angeles. This year's event raised more than $1 million for the cause.
"It's for Children's Hospital Los Angeles, which I am a nurse there, so it's really close to my heart," said participant Lauren Windham. "Anything I can do for children's cancer, it's great."
Most of Sunday's participants say they will be back again next year.