Initially, Universal Studios had considered an injunction because of the film's satirizing, but the lawsuit was cancelled and allowed to continue the film for its release date after Steven Spielberg's gave a positive thought for the film in advance. Released on August 3, 1978, the film was a critical and commercial success and has later achieved a cult following. Piranha was followed by a sequel, Piranha II: The Spawning, in 1981, and two remakes, one in 1995, and another in 2010, which spawned its own sequel in 2012.
Two teenagers come upon an apparently abandoned military installation. They take advantage of what appears to be a swimming pool to skinny dip. The teenagers are attacked by an unseen force and disappear under the water. A light activates in the main building and a silhouetted figure investigates the screams, but is too late to help.
A determined but somewhat absent-minded insurance investigator named Maggie McKeown is dispatched to find the missing teenagers near Lost River Lake. She hires surly backwoods drunkard Paul Grogan to serve as her guide. They come upon the abandoned compound, which functioned as a fish hatchery before being militarized. They discover bizarre specimens in jars and indications of an occupant. Maggie locates the drainage switch for the outside pool and decides to empty it to search the bottom, but the moment she activates it a haggard and frantic man begins to panic and attacks her, attempting to stop the draining until he is subdued by Grogan. The two find a skeleton in the filtration trap of the empty pool, and learn it was filled with salt water. The man awakens and steals their jeep, but crashes it due to his disorientation, and is taken to Grogan's home where they spend the night. They take Grogan's raft down the river, where the man wakes up and tells them that the pool in the facility was filled with a school of piranhas, and that Maggie released them. They are skeptical until they hear a dog barking and they come across the corpse of Grogan's friend Jack, who has bled to death from an attack on a fishing dock.
The man reveals himself to be Doctor Robert Hoak, lead scientist of a defunct Vietnam War project, Operation: Razorteeth, tasked with engineering a ravenous and prodigious strain of piranha that could endure the cold water of the North Vietnamese rivers and inhibit Viet Cong movement. The project was shut down when the war ended, but some of the mutant specimens survived, and Hoak tended to them to salvage his work. Grogan realizes that if the local dam is opened, the school will have access to the Lost River water park, and the nearby summer camp where his daughter Suzie is in attendance. They encounter a capsized canoe with a boy whose father has been killed by the fish. Hoak rescues the boy but suffers mortal injuries when the school attacks him; he dies before he can reveal how to kill them. Blood from Hoak's corpse causes the piranha to tear away the raft's lashings, and they barely reach shore. Grogan stops the dam attendant from opening the spillway and calls the military.
A military team led by Colonel Waxman and former Razorteeth scientist Dr. Mengers feed poison into the upstream section, ignoring the protests that the fish survived the first attempt. When Grogan discovers that a tributary bypasses the dam, Waxman and Mengers quarantine them to prevent the agitated pair from alerting the media. After they escape, Waxman alerts law enforcement to capture them. The school attacks the summer camp during a swimming marathon, injuring and killing many children and a supervisor. Suzie escapes due to her fear of water, and aids her camp mates in escaping.
The school continues downriver. Waxman and Mengers arrive at the water park to intercept Grogan and Maggie, but the piranha attack the resort and kill many vacationers and Waxman. Grogan and Maggie commandeer a speedboat and rush to the shuttered smelting plant at the narrowest point of the river. Remembering the empty facility pond, Grogan realizes the fish can survive in salt water; if the school passes the delta, they will reach the ocean and spread over the world. He intends to open the smelting refuse tanks, hoping the industrial waste will kill the fish. They arrive at the plant ahead of the fish, but the elevated water level has submerged the control office, and Grogan must go underwater; he ties a rope around his waist and instructs Maggie to count to 100 before pulling him out. Grogan struggles to move the rusted valve wheel when the school arrives and attacks him. The assault hyperadrenalizes him, and he manages to open the valves just as Maggie pulls him to safety. Maggie takes Grogan back to the water park, where a massive MEDEVAC is tending to the victims; his injuries are severe and he is seen in a catatonic state.
Mengers gives an on-site television interview, providing a sanitized version of events and downplaying the existence of piranha. Her voice is heard carrying out over a radio on the shore of a West Coast beach. As she says "there's nothing left to fear", the piranha's characteristic trilling sound drowns out the waves on a beach.Bradford Dillman as Paul Grogan
Heather Menzies as Maggie McKeown
Kevin McCarthy as Dr. Robert Hoak
Keenan Wynn as Jack
Barbara Steele as Dr. Mengers
Dick Miller as Buck Gardner
Belinda Balaski as Betsy
Bruce Gordon as Colonel Waxman
Paul Bartel as Mr. Dumont
Melody Thomas Scott as Laura Dickinson
Barry Brown as Trooper
Shannon Collins as Suzie Grogan
Shawn Nelson as Whitney
Richard Deacon as Earl Lyon
John Sayles as Sentry
The film was released theatrically in the United States by New World Pictures in August 1978. Given the proximity to Jaws 2, Universal Pictures had considered an injunction, but Spielberg convinced them otherwise.
In 2004, New Concorde Home Entertainment released the film on special edition DVD. This version is currently out of print.
In 2010, as a tie-in to the release of the remake, Shout! Factory re-released Piranha on DVD and Blu-ray.
On 13 March 2015 the film screened in a R rating Ultimate Edition presented by the Fangoria Magazine and the speciual guests Rebekah McKendry, curator Mike Williamson and origin actress Belinda Balaski.
Based on reviews from 25 critics collected by the film review aggregator Rotten Tomatoes, 72% gave Piranha a positive review. Steven Spielberg called the film "the best of the Jaws ripoffs".
Piranha was first remade in 1995, and this version was also produced by Roger Corman and originally debuted on Showtime. It used footage from the original for certain sequences.
Another remake of the 1978 film is directed by Alexandre Aja, who again works with filmmaking partner Grégory Levasseur; the two have worked on other genre films as well, including the 2006 remake, The Hills Have Eyes. Distributor Dimension Films' Bob Weinstein told Variety, "We will maintain the fun and thrilling aspects of the original film, but look forward to upping the ante with a modern-day twist." Piranha 3D was theatrically released in the United States on August 20, 2010 and is in 3D.
Dimension had been developing the remake of the 1978 Joe Dante film Piranha for over a year. It intended to have Chuck Russell, who previously reworked the 1988 version of The Blob, direct the film before taking on Alexandre Aja. Aja intended to rewrite a previous script from Josh Stolberg and Pete Goldfinger. Aja explained, "My goal is not to remake Piranha, but to create a completely new adventure paying homage to all the creature films [...] I am very proud to follow the path of Joe Dante and James Cameron in the Piranha franchise and look forward to working with Greg Levasseur to write, produce, and direct such a fun and gory thrill ride." The film's cast includes Elisabeth Shue, Christopher Lloyd, Richard Dreyfus, Adam Scott, and Jerry O'Connell.