* {{Corpsing}}: When [[spoiler:Derrick's]] half-eaten body is brought onto the boat, Laura's actress can be seen grinning instead of looking horrified.
* NotScreenedForCritics: But it got a 74% Fresh rating on Rotten Tomatoes despite this.
* ReleaseDateChange: Originally scheduled for a July 24, 2009 release, then was pushed back eight months to March 19, 2010, then April 16, 2010. In January 2010, it was published that Dimension Films was looking for a late summer release instead of April, August 27, 2010 was the new date. The film was finally released on August 20, 2010.
* RoleEndingMisdemeanor: Gianna Michaels was a last minute replacement for Natasha Nice, who got arrested while working on a hardcore movie prior to the shooting of her scene, and was unable to do the small part Michaels plays in the picture.
* ThoseTwoActors: Creator/ChristopherLloyd and Creator/ElisabethShue [[Film/BackToTheFuturePartII once]] [[Film/BackToTheFuturePartIII again]] star alongside each other.
* SparedByTheCut: A deleted scene reveals Cameraman Andrews was originally going to be killed on-screen by the piranhas. Since this scene was deleted, his character appears to vanish without a trace. Paul Scheer reprises his role in the sequel, but it's unknown if his scene was cut for this reason or another.
* TroubledProduction: In 2018, Creator/AlexandreAja [[https://moviecrypt.libsyn.com/ep-288-alexandre-aja revealed]] in the podcast ''The Movie Crypt'' that post-production on the film was a nightmare. In short, Dimension Films attempted to [[CuttingCorners cut corners]] on the CGI by hiring the cheapest VFX artists they could find, including complete newbies to the industry who'd never worked on a movie before. It showed; by June 2010, just two months before the film was supposed to be released, not a single CGI piranha was finished. Aja threatening to pull an AlanSmithee finally convinced Bob Weinstein to hire every VFX artist Dimension could get their hands on to finish the film. Harvey Weinstein also hated the film, expecting a more serious horror film like ''Film/{{Jaws}}'' and instead getting a HorrorComedy that he called ''Jaws Gone Wild''.
* WhatCouldHaveBeen: The Blu-Ray reveals two abandoned sequences storyboarded that are even more over the top than some of the Piranha attack sequences in the movie. One of the sequences was filmed for the sequel.
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