It stands to reason that a movie about a haunted pool swallowing children and adults would absolutely have to have extraordinary underwater photography, just by design.

“Night Swim” manages that, so a tip of the scuba mask to underwater director of photography Ian S. Takahashi (“Under the Silver Lake,” “The Lost City”). The scenes beneath the surface, looking up or looking down, with victims struggling against whatever is after them, are just beautifuly lit and shot.

The movie? It’s middling, even by early January horror release standards. A few moments of suspense, a belated “Maybe I should play this guy as funny/crazy” decision by leading man Wyatt Russell, a little “It!” and not much else in terms of inspiration, and effects that don’t add to the fear quotient sends this sinker down for the third time.

In 1992, a little girl (Ayazhan Dalabayeva) is lured to the pool in her bunny slippers in the middle of the night so that she can retrieve her kid brother’s toy boat — which had disappeared and is how circling the pool, under its own power.

Before wee Rebecca can scream “Toy boat toy boat toy boat,” nothing but a floating bunny slipper remains.

Decades later, and third baseball Ray Waller (Russell, son of Goldie and Kurt) and his family decide to move into the house with the pool in back. He’s dealing with the onset of multiple sclerosis, his doctor is empathetic but no-nonsense.

“Forget baseball.”

He’ll have to live off educator wife Eve’s (Kerry Condon of “Three Billboards,” “The Banshees of Inisherin” and TV’s “Ray Donovan) insurance and income, rooting for his aspiring swimmer daughter (Amélie Hoeferle) coaching his little boy (Gavin Warren) in America’s Pastime, despite the crutch he now uses.

That pool? That’s therapeutic. Ray soon proves that as his symptoms abate and he feels as if he might get another shot at the Big Leagues, all thanks to the “land of sky blue waters” that fills that pool.

But the wife and the kids soon have other experiences when they swim — voices from the overflow drains, items disappearing, hallucinations about who is peering over the edge down at them, mistaking swimming down for swimming up, living corpses sneaking up on them, holding them under water.

“Marco Polo” becomes a game with a menacing edge under those conditions. But only slightly.

The “rules” of writer-director Bryce McGuire’s world are explained in the third act, and don’t add up to much.

The build-up towards a “Jaws” style “pool party” that’s as ill-advised as opening the Amity beaches on July 4 is mostly-botched. There just isn’t much suspense in the death-comes-from-the-pool scenes that we haven’t seen in the film’s trailers.

But the underwater attacks, escapes and revelations are gorgeous to look at, with a lot of the cast and the effects crew immersing us in the perils of a pool, even if they never get a handle on how frantic drowning and near-drowning is as an experience.

Any more than anybody REALLY gets a handle on how one would likely respond to the terrors of facing something supernatural and evil.

One or two “Minnesota” touches, provided by the dizzy realtor (Nancy Lenehan), and Russell deciding to occasionally make the increasingly unhinged Ray comical as well as possessed and evil aren’t enough to save it.

“Night Swim” never amounts to much more than a dip in lukewarm water.

Rating: PG-13 for terror, some violent content and profanity

Cast: Wyatt Russell, Kerry Condon, Amélie Hoeferle, Gavin Warren, Nancy Lenehan, Eddie Martinez, Ayazhan Dalabayeva and Jodi Long.

Credits: Scripted and directed by Bryce McGuire. A Blumhouse/Universal release.

Running time: 1:38