In response to a court offer, Briles, 35, had pleaded guilty to one felony count of child abuse and endangerment and one misdemeanor count of resisting an officer, the statement said.
Briles had previously claimed that he had done nothing wrong.
He told CNN affiliate KTLA in August that "we were having fun, it was a harbor cruise!" He said he did not hit his son and he "did nothing except jump in the water with my kid."
Briles, who's divorced, was on the tour boat on a Sunday afternoon in August with his two sons, ages 6 and 7, when he got into an argument with his current girlfriend, sheriff's office spokesman Jim Amormino said in August.
The boat, named the Queen, takes passengers past Newport Beach houses that are or were occupied by celebrities, including the home where the late John Wayne lived, Amormino said.
Briles's 7-year-old son became upset about the argument and started crying, Amormino said.
The defendant was "under the influence of alcohol" at the time, according to the district attorney's statement.
"The father took the boy to the bow of the boat and told him, 'If you don't stop crying, I'm going to throw you overboard,' " Amormino said.
"And he hits the kid a couple of times," Amormino said. "The boy is crying. He picks him up and throws him overboard. They are in the middle of a harbor, and there is a lot of boat traffic."
The first mate on the Queen "stalled the boat and maneuvered it to protect the child from being struck by another vessel," the district attorney's office said. "The captain threw the crying child, who was treading water, a life ring."
The boy's life was endangered several ways, the authorities said.
