Four people died and some two dozen people were injured after a boat got into trouble off the coast of San Diego in a suspected smuggling operation.
The overcrowded 40-foot (12m) cabin cruiser broke up on a reef near Point Loma on Sunday morning, tipping some 30 people into the water, officials said.
A major rescue operation was launched to help the injured on shore and retrieve seven people from the sea.
Officials said the boat captain was in custody on suspicion of smuggling.
"Every indication from our perspective is that this was a smuggling vessel used to smuggle migrants into the United States illegally," Jeff Stephenson, Supervisory Border Patrol Agent, said.
"We haven't confirmed the nationality of the people involved, but our agents are with many of them at the hospital and the man who we believe was the operator... The investigation's still unfolding."