Revealing mistake: As soon as the three survivors are coming out of the lab through the hatch underwater, they all signal each other to rise to the top. Look at Safron Burrows, her cheeks are full of air and you can almost see the surface above her head. You can also see the exact same shot when she is about to be eaten by the last shark. And what's with that hand gesture - to cut or for the shark to stop?
Revealing mistake: When the sharks first attack and bite off the man's arm - you can clearly see his arm under his shirt as he's scrambling away from the water.
Factual error: Near the beginning when the boat pulls up and the guy on the boat tells the blond convict he's got a beauty 13 foot "Tiger shark" that's up in some sort of sling, the so called tiger shark is actually the same robot mako shark from the rest of the movie, just with stripes on it. Tiger sharks have a blunt rounded nose, not a pointed one like a great white.
Revealing mistake: In the scene where L.L. Cool J. is in the flooded kitchen and the shark comes in through the door, he climbs up a shelf, then falls in the water, then climbs out again. Before he makes his way to the oven you can clearly see that under his pants he is wearing knee pads.
Revealing mistake: In the shot when the helicopter is about to crash into the building, take a look at the blade. There is a wire holding the helicopter.
Factual error: A double oven has a double or triple insulating wall between ovens, not a single sheet of flimsy steel.
Continuity mistake: When the shark is brought up to put the needle in his head he bites off the guys arm leaving only a bit left there, yet when they are wheeling him to the helicopter you see that he's got more arm than before.
Continuity mistake: Towards the end of the movie, the Preacher stabs the shark in his left eye with his cross, causing it to bleed. Later, in the next scene when shark returns to eat Susan, its eye is intact.
Continuity mistake: Near the end scene, when the three characters came to the surface, L.L. Cool J. was taken by the shark. When he was taken underwater and when he surfaced, the shark had him in her mouth on the right side. When they went under again and resurfaced, L.L.Cool J. was on the left of the shark's mouth. What? Did the shark not like him on the right side so she switched him underwater?
Other mistake: When the shark first smashes the glass with the gurney carrying the man who was first bitten and failed to escape in the helicopter, he releases the gurney about 50 feet away from the glass. How could the gurney maintain its speed underwater?
Continuity mistake: When McCallister cuts herself and jumps into the water, you see blood in the first shot. Then when she is swimming and wading etc., there is no sign of blood at all.
Factual error: Since the water was always waist high, how could the huge sharks swim inside? Not to mention the corridors...
Continuity mistake: When Carter is sitting in front of one of the small hatch-like doors around the time that they were climbing the ladder to escape from the rising water, one can clearly sea that the door is no more than twice the width of Carter (4 feet at most) yet the 45 foot shark about 10 to 12 feet wide seems to have no trouble squeezing through.