Piranha (1978)

Continuity mistake: In the scene where the kids at the Lost River Lake Resort are being attacked by piranha fish, Brogan's daughter Susie is hiding under a blue boat. She tries to lift the boat so she can use it to rescue her friends. It's too heavy for her, so she uses an inflatable boat instead. As she launches the inflatable off the jetty, you can see the blue boat in the water beside the jetty. Moments later, Brogan arrives and picks up the boat from where it was when she was hiding under it.