Piranha

Genetically engineered piranha, bred by the military for the Vietnam War and left in a mountain pool, are released into a river that runs to a summer camp and a new resort.

Roger Corman produced it to ride Jaws, and Spielberg reportedly liked it enough to drop a threatened lawsuit. It launched Joe Dante, who directs it with real wit, and John Sayles wrote it, which is why the satire, the military cover-up, the resort owner who will not close the water, has actual bite.

The effects are cheap and the film knows it, playing the horror and the comedy at once, and the camp massacre is genuinely nasty for a film this playful.

It is the best of the Jaws imitators by a distance, and it started the careers of several major film-makers.

Dante and Sayles went straight from this to The Howling.