“God’s Creatures” is a quietly gripping Irish coastal drama kept afloat by a powerful, understated performance by Emily Watson, who lets us into the unseen agony of a mother’s questions unasked.

Co-directors Saela Davis and Anna Rose Holmer bathe their film in the overcast gloom of a fishing town where men sometimes drown, almost as a local tradition.

“It’s bad luck to know” how to swim, is how matriarch Aileen O’Hara (Watson) describes it.

“If they can’t swim, they won’t jump in and help anybody else,” is daughter Erin’s (Toni O’Rourke) more cynical view.

Shane Cowley’s script brings a little sunshine into this world, where oystermen regularly misjudge the tide in their heavy waders and get pulled down in a flash when the water laps high enough. With every death, the whole village shuts down and everyone falls into mourning.

But Aileen’s prodigal son Brian (Paul Mescal of “The Lost Daughter”) returns, after years out of contact far off in Australia. Aileen’s first unasked question is why he’s come back, what went wrong Down Under. Her daughter might be blunt enough to wonder more than that. His first love, the now-married Sarah (Aisling Franciosi), is almost too shattered to let herself care.

But Mum just brings him in, watches him comfort her near-catatonic father and reach an uneasy truce with his leery Dad (Declan Conlon) and tries to help. He wants to work old Paddy’s long-idle oyster beds? Let her swipe a few bags of seed oysters from Guiney’s Atlantic Sea Foods. He might be encouraging old feelings in unhappily-married Sarah. Mum’ll turn a blind eye.

Then something happens, something serious, made all the worse by the fact that it happens in a tiny town where everyone knows everyone else. And Aileen finds herself with one other question not to ask.

The twice-Oscar-nominated Watson, most recently lauded for her work on TV’s “Chernobyl,” creates an easy, motherly rapport with Mescal and O’Rourke. Aileen may be a fair-minded supervisor at the sea food processing plant, but these two are too old to listen to any advice she has for the wandering son or new single mom.

There’s even a hint of a lifetime of abuse from her almost speechless aged father (Lalor Roddy). Aileen bears it, and Brian’s shortcuts in life and work, without much protest.

The script sets us up for tests and heartbreaks, showing us the ritualistic grief that comes with a drowning early in the film, with Franciosi giving us a taste of Sarah’s bitterness and vulnerability — she also sings at funerals — and Watson serving up stoicism barely betrayed by weary, her edge-of-tears eyes.

Davis and Holmer, veterans of assorted jobs behind the camera, soak up the atmosphere of County Donegal, painting their portrait of this world in careful, considered strokes — the green-walled pub where Guinness and G&Ts are poured, songs are sung and community is made and shattered, the blessing of the skiffs of the fishing “fleet,” the grueling and dangerous nature of what looks like simple work, harvesting oysters between changes of the tide.

Its modest ambitions notwithstanding, in “God’s Creatures” they’ve created something like the perfect film for autumn, a beautiful portrait of intimacy and warmth and family tinged with a chill that can only lead to tragedy.

Rating: R, violence, profanity, smoking

Cast: Emily Watson, Paul Mescal, Aisling Franciosi, Declan Conlon and Toni O’Rourke

Credits: Directed by Saela Davis and Anna Rose Holmer, scripted by Shane Cowley. An A24 release.

Running time: 1:41