San Joaquin County authorities say the four men were on a 14-foot aluminum boat crowded with ten people when it tipped over. The accident happened around 12:30 yesterday morning in a canal near Tracy.
None of the men on board were wearing lifejackets, but six were able to swim ashore.
The operator of the boat -- 43-year-old Daniel Cordova -- was arrested on suspicion of boating while intoxicated.
Authorities say he could also face vehicular manslaughter charges.