Revealing mistake: When Fin decides to help the kids on the bus and says, "Water's rising, I'm gonna go up to the bridge and rappel down," two shots later the camera zooms in on Fin's car up on the bridge, but the problem is that this shot is shown in reverse - all the vehicles in both lanes are going backwards.
Continuity mistake: While Fin's talking to Baz about Plan B, when Baz tells Fin to stay with his family Fin turns around to look at them in the background, but in the shot of Fin's family we see Fin there holding propane bottles, even though he's actually still talking to Baz elsewhere. He cannot be in two places at once.
Other mistake: While Baz, Fin, and the others are on their way to Matt at Van Nuys Airport, they're blocked in every direction by police cars, and there's a closeup of the rearview mirror which shows their vehicle's clear view through the back windshield, so we can see the police patrol car behind them. The problem is that the view out the vehicle's back windshield is not clear, but actually obscured by camo netting.
Other mistake: The Hollywood Sign has 9 letters - "HOLLYWOOD." When the Hollywood letters are flying through the air toward Fin and the others, there are at least 8 letters in the sky, but when Nova, Fin and the others are driving away from the bridge we can see "L, Y, and O" still up on Mount Lee, which means that only 6 letters should have been in the air earlier.
Deliberate mistake: When a shark lands in front of TCL Chinese Theater (Grauman's), it leaves a shark shaped indentation on the ground right above the square concrete block with Steven Spielberg's signature, handprints and shoeprints. Fun homage to the 'Jaws' director. But in fact the actual concrete block, dated 5-16-84, is rectangle and shared by both Spielberg and George Lucas, and it's also not located at the center of the forecourt in front of the doorway.
Continuity mistake: At Fin's house, at the bottom of the stairs there's a table and a ceramic lamp at the corner of the walls, and when Collin shouts for Fin's help he's standing at that corner and the lamp has been knocked over under the water, but after Collin's demise the lamp is upright and back in place.
Continuity mistake: Once April and Claudia are in Fin's car, when Fin says, "My luck, sharks," it's raining and the wipers are on, swishing back and forth, but in the next closeup as Nova says, "Mine too," the front windshield is perfectly dry and the wipers are not on, then next shot it's back to rain and swishing.
Revealing mistake: While Matt and Nova are up in the chopper, Baz loads the vehicle then asks Bobby how the front end is looking, and in the next overhead shot we can see that one of the center spokes has been removed from the front of the vehicle, but when Luellyn pushes Bobby out of the way Luellyn is skewered by that non-existent spoke - which was digitally added. The real spoke is back on in later shots.
Other mistake: After the bridge rescue, when the wind picks up the letters of the Hollywood Sign are uprooted and take flight, and we see the "Y" flying through the air, but later when they're driving away we can see Mt. Lee behind the car with the remaining letters, and the Y is still mounted there.
Continuity mistake: Towards the end of the bridge rescue scene, Fin Shepard cuts the rope below him to escape from the shark climbing up. The shark falls into the rushing water. The problem with this is that the school bus that Fin climbed out of is missing. The bus should be visible directly below Fin and the shark. (00:47:16)
Continuity mistake: When Fin saves his friend from the shark, in the closeup he has his arm around Fin's shoulder and in the far away clip he doesn't. (00:13:05)