Chris Lozano, 16, had just stopped surfing near the Ventura Pier on Friday when he heard a cry for help from a girl who had gotten pulled out by the tide while swimming.
Worried the waves would slam Maya Harding, 11, into the pier, Lozano used training he learned in the Young Marines program to save her.
"She was shaking. She was trying to kick, and I told her, 'If you are going to kick, then we are both going under,'" said Lozano.
"He grabbed me by my waist and held me, and he said, 'You're OK. Breathe in and out. Breathe in and out,'" said Harding.
Lozano left before Harding's family could thank him, but the two families hope to meet each other.
The 16-year-old now knows what he wants to do when he grows up. He said he wants to be part of the Coast Guard.
ABC News and CNN contributed to this report.