Though his name is all over the advertising as the film’s executive producer, it’s not clear how much creative input James Cameron actually had on “Sanctum” beyond lending out his “Avatar” 3D technology. Sure, it’s the sort of story he’d go for, what with its many underwater scenes, and it is based on a harrowing incident that really happened to one of his frequent collaborators, Andrew Wight. But did Cameron have anything to do with the actual movie? If he did, he should downplay it.

“Sanctum” isn’t bad, but that’s not for lack of trying. Set in a vast New Zealand network of caves from which intrepid explorers must escape after flood waters threaten, it has interchangeable characters and template dialogue. The obligatory emotional hook is the reconciliation between a father and son who are among those trapped. The whole thing falls somewhere between the disaster genre and the horror genre … but it’s not campy enough for the former, and not scary enough for the latter.

Our hero, somehow, is Josh (Rhys Wakefield), a thin, willowy lad whose gruff father, Frank (Richard Roxburgh), is one of the foremost experts on cave diving. (That’s spelunking, but where some of the areas to be spelunked are under water). Josh has been dragged along on these excursions his whole life, yet can never seem to please his father, who runs a tight crew and does not abide foolishness.

This particular venture is being funded by Carl (Ioan Gruffudd), a millionaire playboy and adrenaline junkie who has come to check out the progress with his girlfriend, Victoria (Alice Parkinson). Josh greets them at the surface, and they all descend to where Frank and his team have been poking around for several days, a couple kilometers down, in an incredible labyrinth of caves and underground rivers.

Somebody dies in an accident, but that’s just to keep our attention. That’s a placeholder death. The real emergency arises when the exit is blocked and the group must find another way out, swimming and climbing through caves that have not been fully mapped.

I’ll say this much for “Sanctum”: a lot of the photography is gorgeous. Whether above water or below, director Alister Grierson and cinematographer Jules O’Loughlin capture some astonishing images of natural beauty. Whatever line there is between real locations and sound stages is imperceptible.

But Grierson has trouble staging the action scenes, which must have been a logistical nightmare. (This is Grierson’s second feature, the first to be seen outside his native Australia.) The geography — the spatial relationships between objects — is often unclear, and with so many characters in wetsuits and scuba gear, it’s frequently hard to tell who’s who, or who’s fighting with whom, or what has happened to put them in danger. Then again, even when we can see their faces distinctly, the characters are generally anonymous, save for Josh, Frank, Carl, Victoria, and a guy named George (Dany Wyllie) who has decompression sickness. (Yeah, that’s five people. There are like seven others, though not by the end, if you know what I mean.)

The screenplay is negligible. Credited to producer Andrew Wight and first-time writer John Garvin, it offers only the barest of character motivations, and no memorable lines —

OK, maybe one: “I am not wearing the wetsuit of a dead woman!” Not memorable for the right reasons, though.

OK, maybe two: “There is no God down here!” But ditto.

— and you get the feeling nobody thought it was necessary to flesh things out, that the basic scenario would be compelling enough to carry the film. There are moments of surprise and tension, but not many, and they aren’t surprising or tense enough to make the movie anything more than something you watch because nothing else is on.

C (1 hr., 49 min.; R, a lot of harsh profanity, some violence and grisly images.)