At least one vehicle went over the edge and lay sideways in the water, pictures posted by the Louisiana State Police showed.
The search for victims from the chain-reaction accident continued for hours after the crash, the state police said on Facebook.
The accident closed Interstate 55 in St. John the Baptist Parish.
The massive crash was one of several accidents in the area due to heavy fog, police said.
He also urged drivers to take care from the "dangerous combination of wildfire smoke and dense fog."
Persons:
John, Baptist, John Bel Edwards, Daniel Trotta, Sonali Paul
Organizations:
Reuters . Louisiana State Police, Handout, REUTERS Acquire, Louisiana State Police, Facebook, National Weather Service, Thomson
Locations:
St, Baptist Parish , Louisiana, U.S, Louisiana, New Orleans, Maurepas, Baptist Parish