Continuity: In several of the "summer" camp scenes it is clearly early spring. Many of the trees still have no leaves.
Revealing mistakes: The speed boat is racing in the lake at full speed. The shot cuts to the skiers POV looking at the boat and the pull rope is slack and there isn't any tension on the line at all.
Continuity: The water skier is doing his runs on the river. He is wearing a orange life jacket, but when he falls into the water the jacket is yellow.
Continuity: The position of the plane ticket in Earl's hand as he gives it to Maggie.
Continuity: As Dr. Hoak is attacked by a piranha, he gets onto a raft and his sweater alternates between torn and intact.
Audio/visual unsynchronized: When Dr. Robert Hoak drives away in the Jeep, the tires make squealing sounds, as if it was driving on asphalt, when in fact it was a gravel road.