Piranha (1978)

As another entry in the pantheon of killer monster films, Piranha is the tale of a school of deadly genetically altered piranhas who are accidentally released into a river, threatening a summer camp, resort, and a large number of local inhabitants. With its woodsy setting, it reminds me a lot of Grizzly though it seemed to manage the balance of horror and campiness better. It smartly includes skinny dipping teenagers, a mad scientist, abandoned governmental experimentation, and plenty of carnage. It also knows not to over-show the actual fish, instead relying on pools of blood and the imagination of the viewer.