James Cameron ‘I’m king of the [water]world!’

Should you ever meet James Cameron, look at his fingers. We’d bet anything they’re seriously pruned.

The filmmaker has spent more time underwater than the lost city of Atlantis. Whether it’s his deep-sea documentaries, including “Ghosts of the Abyss,” “Expedition: Bismarck” and “Aliens of the Deep,” or feature films, such as “Titanic” and “The Abyss,” Cameron has always been drawn to the world of waves.

On Friday, he wades in again with “Sanctum.” Cameron, an avid scuba diver, produced the thriller about a group of Australian explorers who are forced to swim their way out of a cave after a freak flash flood.

The experience is claustrophobic, dark and wet. Or as Cameron would probably call it, “heaven.”

The story was inspired by actual events. In 1988, Andrew Wight — a longtime Cameron buddy and the film’s co-writer — was leading a diving expedition into an underwater cave system beneath Australia’s Nullarbor Plain.

“A freak storm hit the area and what started as a trickle of water into the cave turned into a torrent, which then started to collapse the entrance of the cave,” Wight says.

Luckily, all survived, and in 2006, he pitched to Cameron the idea of making a film loosely based on the experience.

Cameron was, of course, game, but he had one stipulation: that the film be conceived and shot in 3-D, not hurriedly post-converted, like many movies these days, including “Clash of the Titans” and “The Green Hornet.” After his experiences with “Avatar,” Cameron believes that 3-D is the future.

The only problem was, “Sanctum” would have the same budget as the catering on “Avatar,” as Wight joked.

“Truthfully, one of the things that attracted me to this particular production was the challenge of shooting high-quality, live 3-D on a relatively modestly budgeted film,” says Cameron, who as producer had to monitor the bottom line. “Compared to ‘Avatar,’ all movies are modestly budgeted, but this movie was made for one-fifteenth or one-twelfth of what ‘Avatar’ cost.”

Not that they completely skimped. Elaborate underwater sets were built in a Queensland, Australia, tank that measured 130 feet long, 100 feet wide and 23 feet deep. It held 2 million gallons of water.

The actors spent weeks in diving training, because director Alister Grierson insisted on as much realism as possible.

“It was pretty hard-core diving to say the least, and it’s amazing to think that many of the underwater stunts you see in the film were done by the actors themselves,” says co-writer John Garvin.

The shoot’s physical requirements didn’t come without some bellyaching from the cast.

“If they’re not grumbling, you’re not doing it right,” Cameron joked.

By the time the cameras got rolling, Richard Roxburgh, who plays expedition leader Frank McGuire, was capable of doing stunts at which some professional divers might balk.

“On some days, I would think, ‘If I mess up this face rebreather exchange in this particular stunt sequence, then I’m going to drown,’” he says. “Even though there’s a stunt safety person who’s only four or five meters away, it was genuinely hard work and frightening.”

Great work. Now someone get that man a towel.