Plot hole: At the beginning (and the end of course) of the movie, Denzel's phone rings - the one on the Denzel in the body bag. First off, a cell phone that was submerged in water like that should not ring at all. Secondly, the phone the live Denzel has on him ring if someone calls that number in his reality

Factual error: The stolen ambulance had windows on both the driver and passenger sides of the patient compartment. Ambulances don't have windows on the driver's side, and rarely have them on the passenger side, since these walls are used for cabinets.

Continuity: The colors of the lightbar on the ambulance stolen by Agent Carlin keep changing. Sometimes they are red and clear, other times they are red and blue (which wouldn't be allowed in Louisiana - blue is reserved for law enforcement).

Continuity: In the scene where Denzel Washington is underneath the bridge, he uses his left hand to swipe the substance, while Val Kilmer holds his right hand. However, in the next shot, he sniffs his right hand to determine what the substance is, while his left hand appears to be in his pocket.

Factual error: Near the end of the movie, the truck is launched into the Mississippi River, which has essentially zero visibility at the shallowest of depths at all times; thus the nickname "Big Muddy". In the movie, the river is crystal clear, even several feet down.