Troopers responded to the crash on U.S. 90 just east of Franklin at around 1:05 p.m.
The truck, driven by Roderick Preston, 34, was fully loaded with sugar cane and was eastbound on U.S. 90 when Preston lost control and exited the left side of the roadway and entered the median.
After entering the median, the vehicle continued across the westbound lanes and the westbound frontage road before entering the Hanson Canal, where it came to rest with the cab totally submerged.
The vehicle was recovered from the canal at 11 p.m. Saturday.
It is unknown if Preston was wearing his seatbelt. He was pronounced dead at the scene by the St. Mary Parish Coroner.
Routine toxicology tests are pending and the crash remains under investigation.