The Abyss (1989)

Factual error: When Lindsay is being revived after Bud towed her back to Deepcore, I understand why the CPR being done isn't exactly correct(due to the fact the actress isn't really dead) but the filmmaker neglected to notice that when the crew proceeds to shock Lindsay, she is wet and on a metal floor. Not only would she be shocked, the entire crew around her would be shocked as well.

Factual error: There are no fish in the entire movie except the scene in the sub with the crabs on the dead guy. Phytoplankton are attracted to artificial lights which means a whole food chain develops around submarine structures like the Deepcore rig - just look at any film of the shoals of fish feeding around the legs of an oil rig. You'd think there would be fish in the ocean at least every now and then, but we don't see a single one.

Factual error: When disarming the nuke Bud is trying to figure out which one of the two wires to cut. With only two wires running between two separated modules (in the film, one part is unscrewed from the other) any current flowing through one wire must be returned through the other in order to conserved electric charge. Cutting either wire, in this case, will result in breaking the circuit. There is no way for either side of the circuit to detect which wire(s) were cut.