Four men are missing and believed drowned after a boat authorities say was overloaded sank in a California river delta.

San Joaquin County Deputy Sheriff Les Garcia said Sunday that a skiff carrying 10 men sank overnight in a canal of the Sacramento-San Joaquin delta.

Garcia says six of the 10 made it to shore. Four men from Oakland who witnesses said couldn't swim are missing. None wore life jackets.

The boat's 43-year-old operator was arrested on suspicion of boating while intoxicated. He could face vehicular manslaughter charges.