The Sonoma County Sheriff's Department reports that the three were visiting Bodega Head on Saturday afternoon when a wave washed one person into the water.
The two others were trying to rescue their friend when they were caught by another wave and also swept into the ocean.
Two of the waves' victims were able to get back ashore. A boater who witnessed the struggle pulled the third victim's body from the water and administered CPR.
The Coast Guard arrived and took the man to a nearby Coast Guard station, where he was pronounced dead, apparently from drowning. His name was not released.