A family, Gail, Tom, and their child Roarke, decide to take a holiday rafting down a river. As they are setting off they meet a couple of other rafters: Wade and Terry, who appear to be two fun loving guys.

After a day's rafting the family make camp for the night and are joined by Wade and Terry who join with the family in celebrating Roarke's birthday. Wade begins acting suspiciously and Gail decides it would be best to part ways. During the morning's rafting Wade reveals to Roarke that they have a gun with them. As they raft down the river the parents discuss an exit strategy that will allow them to leave the two guys behind and at lunch they attempt to leave on their raft and get away before the two men realize what is going on.

Gail then realizes that an armed robbery that she had heard about was actually carried out by the two guys and their rafting trip is actually a way for them to escape. The family are forced to raft at gunpoint down the rest of the river before they all set up camp for the night. During the night Tom attempts to steal the gun off the sleeping Terry but is seen and has to run into the bushes and to the river. Wade gives chase and believes he has shot him when he hears a loud splash into the water.

It's revealed that Wade and Terry, in order to aid their escape, want to go on down the river to a set of rapids where in recent years one person was killed and another was left paralyzed. Consequently rafting is no longer allowed. Wade and Terry force the rafters down through the rapids despite Gail's repeated attempts to flip the raft and so force the two guys out of the river.

Meanwhile a park ranger, who knows Gail is white water canoeing down the river, bumps into the group; but Wade holds the gun to Gail's back and pretends that everything is OK. Later in the movie he appears again but this time Wade shoots him and he falls dying into the river.

Tom reappears and manages to flip the raft. Gail and Roarke, who have been tied to the raft by Wade, remain in the raft and to get hold of the gun, which had fallen into the water. while Tom is fighting Terry. The struggle ends when Gail throws the bag of money into the water and shoots Wade whose dead body floats off down river. The film ends with the family and Terry (who has been arrested) being helicoptered out.

This is from Wikipedia, which actually described the movie pretty well...