State Police said two of the victims, driver Eddie Cobb Jr., 68, and back-seat passenger Ella Williams, 52, were from Beaumont, Texas and the third, front-seat passenger Brady Brown,was from Columbia, S.C.
Authorities had been on the look out for the trio since they disappeared on a trip from South Carolina to Bossier City to ferry a vehicle back to South Carolina.
A spokesman said troopers in a Louisiana State Police helicopter spotted the floating back bumper of the 2006 Dodge Stratus on Tuesday afternoon but darkness and an approaching storm delayed a search for the car until Wednesday.
Louisiana Department of Wildlife and Fisheries personnel found the vehicle, and Ouachita Parish Sheriff Jay Russell sent his dive team to assist.
State Police said it appeared Cobb was traveling westbound when he left the interstate and traveled about a quarter mile on the median until the car reached a steep embankment and went into the river.
An autopsy will determine if the driver suffered a medical condition that rendered him unconscious. Troopers believe the passengers drowned.