Jason Momoa may be a giant hunk of muscular manhood, but he can’t carry a giant action movie all by himself, and the DC Comics franchise piece “Aquaman” sinks because of it.

Director James Wan, who graduated from horror (“Saw,” “Insidious,” “The Conjuring”) to action (“Furious 7”), aims to give the battle over Atlantis and the ocean realms the look of a full-scale epic on the order of “The Lord of the Rings.” Visually, he nearly succeeds, with scads of sea creatures and humanoids battling in hyper-colorful glory.

But the looks can’t match the story, a hodgepodge screenplay by David Leslie Johnson-McGoldrick (“Wrath of the Titans”) and Will Beall (“Gangster Squad”), with story credit going to Geoff Johns, Wan and Beall. The story’s a mess, with waves of origin story crashing into a tsunami of current action set pieces, resulting in a whirlpool of confusion.

It starts with Tom Curry (Temuera Morrison), a lighthouse keeper who finds a beautiful woman washed up on the rocks. She, we learn, is Atlanna (Nicole Kidman), queen of the ocean kingdoms, on the run from an arranged marriage. Tom and Atlanna fall in love and have a son, Arthur, who’s a mere toddler when the ocean realm sends soldiers to drag Atlanna back to her betrothed.

Years pass, and Arthur is a free-range vigilante keeping the oceans safe from the likes of Manta (Yahoo Abdul-Mateen II), a pirate whose efforts to steal a Russian sub are blocked by Arthur’s actions. Those actions include turning his back when Manta’s father (Michael Beach) is pinned and left for dead.

Arthur learns that his half-brother, King Orm (Patrick Wilson), is mounting a dastardly plan to unite the seven kingdoms of the oceans so he can declare war on the land creatures. Arthur joins forces with Mera (Amber Heard), the daughter of King Nereus (Dolph Lundgren), who has teamed up with Orm. Also on Mera’s side is Vulko (Willem Dafoe), who mentored Arthur as a teen. (Yup, that means more flashbacks.)

Nicole Kidman as Atlanna in a scene from "Aquaman." (Warner Bros. Pictures via AP)

What follows is a convoluted search for an ancient artifact, a quest that sends Arthur and Mera to the Sahara, Sicily and the deepest parts of the oceans. If you were hoping for good company on the way, you’re out of luck, because what the movie delivers is Arthur and Mera alternating between romantic-comedy bickering and Mera making ponderous guilt trips about how Arthur needs to become a leader and “the bridge between the land and sea.”

The cast is serviceable, with the best work coming from Dafoe, who can knock these roles out in his sleep, and Wilson, who’s becoming the Fred MacMurray of his generation: a bland good guy, but a fascinating villain.

But too much of “Aquaman” falls on Momoa’s rippling shoulders, and his surfer-dude personality deflates Wan’s attempts to make him into an aquatic Aragorn. Momoa is good in an ensemble — like in “Justice League” or “Game of Thrones” — but alone, he’s lost at sea.

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★★½

‘Aquaman’

DC Comics’ oceanic superhero gets his own movie, but star Jason Momoa isn’t enough of a screen presence to carry the weight.

  • Where • Theaters everywhere.
  • When • Opens Friday, Dec. 21.
  • Rated • PG-13 for sequences of sci-fi violence and action, and for some language.
  • Running time • 143 minutes.