A shark thriller set in the Caribbean, “The Last Breath” delights in seeing what happens when a bunch of not-very-smart underwater divers become imminent dinner for several of the sea’s most vicious predators.

These divers, old college friends, ignore the most basic rules, are ridiculously careless about monitoring their tanks’ air supply and have absolutely no clue about how to get back to the surface alive.

“They aren’t stupid,” said the film’s Swedish director Joachim Hedén. “I would say they’re deliciously stupid.

“I quite enjoy the progression how this one character who is pushing everything along, how deliciously annoying and reckless he is.”

From its conception, “Breath” would not do the “Aquaman” thing of “Pretend you’re underwater when you’re not.”

“This is all hardcore diving,” Hedén revealed. “Of the main cast, the actors are doing 99% of all the diving and all the underwater work you see in the film.

“There are only three shots in the entire movie where we use stunt doubles for any of the actors. This is the second underwater film I’ve made as a director. Going into the first one, called ‘Breaking Surface’ about an Orca, I had the idea that we could probably get away with 50% using stunt doubles, because that would certainly make the shoot and the schedule easier.

“But I discovered very early, that so much of the actors’ performances are built into their body language. So it’s basically impossible to put a stunt double in for an actor, just because it’s convenient or makes your schedule easier.

“So when casting this movie, I basically started each casting session by giving each actor a 20-minute speech, basically outlining all the reasons why they shouldn’t want to make this movie, because one of the things was that they would have to do basically all of their diving themselves.

“Obviously, actors being actors, nobody said, ‘Oh, I don’t think I want to do that.’ They all jumped at the chance to do it.

“For sure, it was very hard. A tough shoot for everybody involved.”

The divers have discovered the USS Charlotte, a long-hidden WWII warship. Those scenes were filmed in a massive tank.

“Anything and everything you see that takes place outside the wreck in the open ocean filmed in the ocean outside Malta. That’s also where we shot everything that takes place on the surface.

“Then everything and anything that takes place inside the wreck is a big set we built in Belgium.

“Essentially, we’re building a giant bathtub. But when the lights went out, I know for a fact that the actors felt that this was very, very, very real.”

But not the sharks. “Is it a spoiler to say we didn’t throw a live shark in there? That’s true. It’s a CGI shark.”

“The Last Breath” is available on streaming platforms