Goofs

The length of Daniel's sideburns varies throughout the movie. Specially between the hotel room's scenes and the water shots.

Susan and Daniel's snorkels change from the left side to the right side of their heads and back several times (divers always wear them on the left).

Susan's octopus (the yellow spare regulator) goes from being unattached to her BCD to attached and back again throughout the film.

During the movie the tank caps change color, most of the time they are red but sometimes one is green or black.

All four of Susan's hose protectors, where the hoses attach to the first stage, start off being yellow. Towards the end of the film two are either missing or change color.

Susan complains about being stung at the ankle. Jellyfish cannot sting through neoprene wet-suits or booties which both are wearing. Their only exposed skin were their hands and heads.

While its true that Licensed Scuba operators have a passenger manifest on board and make an actual -or several- head counts before weighing anchor and again before disembarking, and leaving two divers behind is preposterous, even in fifty diver "cattle boats" like some in Mexico, this movie IS BASED ON A TRUE STORY and this did, in fact, happen to MORE than just the two this film is based on.

Most divers dive with an SMB (Surface Marker Buoy), also known as a "safety sausage." This is usually a bright neon colored tube that can be inflated using the diver's alternate air source or manually blowing into it. These buoys are typically at lest 2-3 feet long, so they could have extended the tube and waved it, which would have been much easier to spot from a distance away.

When Daniel and Susan first submerge, they are still talking to each other despite having regulators in their mouths.

At the end when a search is started. The sea plane taking off has turboprop engines(Turbine Engine with propellers). The sound is of piston engines.

When Susan asks, "Where's the boat?", they are in the shadow of the camera boat.

When Daniel and Susan are lying on the beach, and Daniel gets up to go for a swim, Chris Kentis is reflected in Susan's sunglasses.

Daniel is bitten at 11.30pm and they are being circled and bumped by a large shark in the dark. The next time we see them is around 8.30 the next morning. Susan would not have survived those 9 hours without succumbing to some combination of physical or mental breakdown, extreme nausea from the movement of the ocean, dehydration and most importantly being bitten by a shark while surrounded by the blood from Daniel's wound.