Beware Boiúna Review: Nelson's Amazon Creature Feature

We meet Brennan Malloy (Logan Marshall-Green), a doctor running a mobile clinic with a small volunteer crew: Lena (Kiana Madeira), the pragmatic nurse who has been down this river before; Alli (Jessica Rothe), the idealistic newcomer; Shawn (Jackson Bews), a young aide with more enthusiasm than survival instinct; and their local guides Miguel and Pedro (Juan Pablo Shuk and Vicente Peña), who know the water well enough to be afraid of it. The mission is simple. Vaccinate a remote village, resupply, go home.

Then the river starts telling them no. Boats go missing. Fishing grounds empty. Something enormous moves under water so dark it looks solid. Boiúna, an ancient predator the locals speak of only in warnings, has woken up to reclaim her domain. What follows is less a hunt than a correction: in the jungle, nature holds absolute power, and she decides who lives and who dies. Callum (Will Close), a corporate fixer with his own agenda, and Raúl (Jaime Newball) round out a cast that gets steadily smaller in the way audiences will immediately recognize.

Nelson directs this thing like a man who has studied every jungle movie and decided to throw out the parts that feel like a theme park. There is no lab. No scientists in crisp white coats explaining the mythology at the ninety-minute mark. The creature stays mostly a shape in the water, a wake, a sound. That restraint is the smartest decision in the film, because what you can't fully see in the first act does all the work in the third.

The performances deserve credit for keeping the whole enterprise grounded. Marshall-Green carries the moral weight of a doctor whose job is to save people and who is now deciding who to abandon, and he plays exhaustion like a man slowly being drained of blood. Madeira is the anchor, funny when she needs to be and terrifyingly competent when the plan collapses. Rothe gets the film's most interesting arc, a gradual erosion of faith that she lands without a single showy moment.

The screenplay, unsurprisingly, is where the film stumbles. Characters make the standard horror-movie mistakes, and the first act takes longer than it should to get everyone on the water. But once the mission goes sideways, Nelson keeps the geography legible - no small feat when half the terror happens beneath the surface - and the sound design does the rest. Every splash becomes a threat. Every silence is worse.

There's also something quietly angry under the surface here, a story about outsiders arriving to do good and learning they are guests on land they never understood. It never turns into a lecture. It just lets the jungle win most of the arguments. The film is in English, and it wears its Hollywood craft proudly, but it respects the setting enough not to use it as wallpaper.

That's the thing about "Beware Boiúna." It isn't out to reinvent the creature feature. It's out to make you hold your breath every time someone steps near the water. It succeeds.

Pros

• Boiúna is used sparingly and effectively, more presence than monster suit
• Strong ensemble work from Marshall-Green, Madeira, and Rothe
• Genuinely oppressive atmosphere and sound design
• Tight 104-minute runtime with no subplot bloat
• A third act that commits to its grim premise

Cons

• Familiar character archetypes and a few too many questionable decisions
• Slow opening act before the mission goes wrong
• Supporting characters like Callum and Raúl get thin material

“Beware Boiúna” earns its place in the long line of river-and-jungle horror by respecting both the water and the audience. It's a Saturday-night crowd pleaser with teeth, best seen loud and with a healthy fear of anything deeper than a puddle.