Police used smoke and tear gas to break up a hostile crowd throwing bottles and cans during a massive brawl at San Diego's Pacific Beach.
Sixteen people were arrested and face charges of fighting and being drunk in public stemming from the Labor Day holiday incident. The size of the crowd was estimated at about 500.
After lifeguards called police about a fistfight, hecklers began throwing bottles and sand at police who were writing citations, prompting a call for riot-control teams, said San Diego Police Department spokeswoman Monica Munoz.
Lifeguards evacuated four towers, removed their uniforms and ran into the water to waiting rescue boats, Lifeguard Service Lt. Nick Lerma said.
"It just got out of control," Lerma said.
It was not immediately known what triggered the fight.
A police helicopter hovered over the beach while officers on the ground formed a skirmish line along the boardwalk.
No officers were injured.
Lifeguards said an estimated 364,000 people visited San Diego beaches on Monday.