Unless you don’t know how to swim, swimming pools simply aren’t scary. Sure, some of them can be pretty gross, depending on how well their owners maintain them. And if bugs or other creatures die in them, that can be disgusting. But mostly they seem like a nice place to relax on a warm summer day. That’s the main problem with Bryce McGuire’s feature about a haunted swimming pool, adapted from a 2014 short film he made in collaboration with Rod Blackhurst. Despite the filmmaker’s best efforts to drum up suspense via the usual jump scares, Night Swim turns out to be just as silly as it sounds.

The short that provided this film’s inspiration had a running time of under four minutes, which sounds exactly right. Unfortunately, the feature version runs 98 minutes, its simple premise gussied up with a backstory mythology that isn’t likely to make Stephen King green with envy.

The story begins with a prologue set in 1992 when a little girl attempts to retrieve a mysterious toy boat from her backyard swimming pool and meets an unfortunate end. Cut to the present day, when we’re introduced to the Waller family: Ray (Wyatt Russell), a former baseball player whose career was cut short by multiple sclerosis; his supportive wife, Eve (Oscar nominee Kerry Condon); teenage daughter Izzy (Amelie Hoeferle, The Hunger Games: The Ballad of Songbirds and Snakes); and 12-year old son Elliot (Gavin Warren, Fear the Walking Dead), who hasn’t inherited his father’s athletic ability.

The family, unaware of the house’s fateful history, makes the mistake of buying the home with the pool, with Ray believing that daily water therapy will help him counteract the effects of his pernicious disease. It also turns out the pool has water provided by a natural spring thought to have healing properties, which indeed seems to be the case as Ray’s condition miraculously improves.

Cue the inevitable disturbing incidents, as the family members prove weirdly determined to stick their hands in every available opening in the pool with predictably unhappy results. Only their pet cat seems to know something is wrong with the pool but not surprisingly it soon turns up missing, its leash floating in the water.

The film attempts to do for swimming pools what Jaws did for the ocean, with Marco Polo and other pool party games suddenly turning sinister and potentially deadly. Except Jaws had a genuinely terrifying monster in the form of a great white shark, while Night Swim has fleetingly glimpsed supernatural creatures of the kind you might see when you get too much chlorine in your eyes. And when they do become more visible as the story goes on, they look like waterlogged Halloween masks.

Swimming pools don’t get haunted without a reason, of course. The one eventually revealed here turns out to be a doozy, dating back generations, having something to do with a demonic wishing well. By the time one of the main characters becomes possessed by whatever is haunting the pool, the film has thoroughly devolved into campiness.