An adventurous couple hiking in the mountains find an abandoned installation and take a swim in the pool. (Something gets them.)
Spunky investigator Maggie (Heather Menzies) is sent to find the missing couple. She teams up with local expert Paul (Bradford Dilman), who is down on his luck after losing his factory job and his wife. They discover the abandoned installation, and Maggie impulsively hits the lever to drain the pool so she can look for evidence. Rogue scientist Dr. Hoak (Kevin McCarthy from Invasion of the Body Snatchers) is too late to stop them, but he does explain that they've just released bioenhanced piranha into the river! (Intelligent piranha. Salt-water-tolerant piranha.)
Can Paul and Maggie get downriver in time to warn authorities and save the children at the waterpark (including Paul's daughter!)? Will greedy developers and corrupt generals even listen to them?
Also appearing in this film are Richard Deacon (Mel from the Dick Van Dyke Show) as Maggie's boss; Keenan Wynn (Col Bat Guano from Dr. Strangelove) as Paul's neighbor; Barbara Steele (Black Sunday) as a government scientist; low-budget movie regular Dick Miller as a waterpark owner; and Paul Bartel (director of Eating Raoul) as an officious girls' camp director.
This was the first in many Piranha movies to come, and is surprisingly focused on the plot and not the girls in bikinis jumping in the water.
The nice thing about piranhas is that you don't need a lot in terms of special effects: some rubber fish on sticks, agitated waters, and fake blood. Simple but it works.
The ending nicely wraps things up by giving Paul a chance to redeem himself, while the fish eat innocents and a few characters who really deserve it.
This movie was one of many imitators to attempt to cash in on the success of Jaws.
Blink and you'll miss it, but some of Dr. Hoak's other experiments appear briefly, an homage to the stop-animation special effects of an earlier era.
In terms of performances: Bradford Dilman is not a favorite of mine, he's playing his character for laughs but does OK in the end; Heather Menzies is adequate in a script that doesn't give her much to do; Kevin McCarthy hams it up; and Dick Miller gives us one of his best performances in a long career.
In terms of gore, this is mild for a horror movie. There is brief nudity of female characters, and young women without bras (well, it was the 70s). Heather Menzies' topless scene was shot by a stand-in (a local waitress).
Can you wargame it? It's pointless, the piranha are irresistible.
I was surprised to like this movie. It's fun, it's suspenseful, it's well done on a limited budget.