Piranha 3DD (2012)

A year after the massacre by prehistoric piranhas in Lake Victoria, Arizona, a massive eradication program has left the lake uninhabitable and the town largely abandoned. At Cross Lake, two farmers search the waters. Piranha eggs laid inside a dead cow hatch, and the farmers are killed and eaten.

Maddy, a marine biology student, returns home for the summer to the water park she co-owns and is annoyed to find that the other owner, her stepfather Chet, plans to add an adult-themed section to the water park that allows nudity. Later that night, Maddy's friend Shelby and her boyfriend Josh go skinny-dipping in the lake, where a piranha fry enters Shelby's vagina. Their friends Ashley and Travis begin to have sex in their van, but Ashley accidentally releases the parking brake, causing the van to roll into the lake. Handcuffed to the van during foreplay and unable to escape, Travis is devoured by piranhas while Ashley, on the roof, calls for help. No one is around to rescue her. The van sinks into the lake and the piranhas eat her.

The next day, the van is dragged out of the lake, where it is found to be empty. Kyle relays this to Shelby, who attempts to call Ashley, only for the call to go straight to voicemail. A distraught Shelby runs off, with Maddy following after her. Maddy finds Shelby sitting on a jetty, and goes on to console Shelby about their missing friends. While they are sitting on the jetty, they are both attacked by a school of piranhas. They manage to kill one, and Maddy, Kyle (a cop and Maddy's ex) and Maddy's coworker Barry take it to marine expert Carl Goodman to examine. He informs them that the piranhas may be moving between lakes and could evolve to travel over land. The trio returns to the lake, where they establish that the piranhas cannot enter the pipes connecting the lake and the water park. While Shelby and Josh are having sex, the piranha in Shelby's vagina bites Josh's penis, forcing him to chop it off. Both are hospitalized but survive. Kyle is revealed to be corrupt and taking bribes from Chet, who is pumping water from an underground river into the water park. Chet orders Kyle to keep Maddy from finding out about his plans.

The adult water park opens with David Hasselhoff in attendance as a celebrity guest. Among the guests are Deputy Fallon and former cameraman Andrew Cunningham, survivors of the previous year's piranha attacks in which Fallon lost his legs. Fallon is there in the hope of overcoming his fear of the water. Maddy attempts to shut the water park down but is stopped by Chet and Kyle. The piranhas enter the area through the pipes and attack, killing many guests. Fallon uses a shotgun leg prosthesis to fight the piranhas, while Hasselhoff rescues a young boy named David. An uncaring Chet attempts to escape, but a low-hanging pendant banner decapitates him.

Maddy instructs Barry to begin draining the pools while she attempts to save those still in the water. However, while rescuing people, she becomes caught in the suction and is dragged down to the bottom of the pool. Barry sees a dolphin-sized adult piranha swimming toward her and throws a litter trident to kill it. After Kyle refuses to save her because of his fear of piranhas, Barry, despite being unable to swim, leaps down and brings her to the surface, at which point Maddy is revived. Thankful to him for saving her, she shares a kiss with Barry, who reveals that he has a crush on her.

Another employee, Big Dave, pours chlorine into the pipes, followed by a lit joint. A resulting explosion kills most of the piranhas. Kyle is also killed by a falling trident. The celebrations are cut short when Maddy receives a phone call from Mr. Goodman, who informs them that the piranha left with him has escaped its tank and can now move on land, to which Maddy replies that she already knows. A lone piranha emerges from the pool and decapitates David while he tries to photograph it. The film ends with the survivors taking pictures of David's corpse with his hysterical mother covered in his blood, and Hasselhoff, overlooking the incident from his chair, calls David a "little ginger Moron".