Two pilots are flying over the amazon rainforest when they are caught in a storm. The two men are forced to land in a lagoon, Which one of the men, pete meyers, recognizes as the legendary “Black lagoon,” a paradise where no one leaves alive. Soon after radioing for help they uncover a large stone triangle covered in vines and moss with strange markings on it. The other man, richard conroy, suspects that it could be from an ancient civilization. Soon they hear a strange roaring sound and the two are attacked by an unseen fish-like amphibious humanoid who drags richard down into the water.
A year later, a geology expedition uncovers the plane with no bodies and nearby they discover the triangular artifact, which is a part of a larger structure nearby that has evidence of being over millions of years old. Expedition leader, Geologist, Dr. Carl Maia orders his two assistants to stay in camp while he visits the Arnold institute.
Carl reunites with his friends and former students, Ichthyologists David Reed, and Kathryn “kay” adams. And they discuss their recent activities before carl shows them the artifact. Upon showing it to their Boss Dr. Edwin Williams, Kay and david convince him to fund a return expedition to the Amazon to look for the other artifacts.
The group goes aboard the tramp steamer Rita, captained by the eccentric captain Lucas. The expedition consists of David, Carl, Kay, Hector Rodriguez, a linguist, and Edwin. They head to the lagoon where before resting for the night. That night the team discuss several things including a supposed legend of a tribe of aquatic men that live in the river. While being watched by the unknown creature.
The next day, the team discovers a large stone and David and Carl go diving to collect rock samples from the lagoon floor. Upon finding that there is indeed similar large stones only larger, one of which is visible from the surface. Upon finding that one, they learn that the stone is actually a door to an underwater passageway that could lead to an underwater temple. Upon entering the passageway they find a corridor which leads to a room with strange artifacts on a large altar. David grabs a goblet on the altar and they begin to head back they catch a glimpse of something following them.
When analyzing the Goblet they determine that it’s made of an unknown material and that the markings on it are runes of an unknown language. Later Kay joins Carl and David when they head back down the passage. Kay splits off when she finds another passage way. The Creature then proceeds to follow her and it touches her ankle. Soon she heads back to find the other two.
Soon when they get back to the ship they find a man in the jungle. When he’s brought to the ship he reveals himself as Pete Meyers, who survived his encounter with the creature. He goes on to tell of his encounter with the creature. He warns them to leave but the expedition refuses, not believing him. The next day they re-enter the passage, this time they find a chamber full of corpses. When they head back to the ship, Hector is attacked by the creature, when the entire expedition arrive on deck to investigate they see the creature in full. Before it proceeds to lunge after kay before Pete collides with the creature as Dr. Maia stabs it with a knife causing the creature to flee into the river.
They attempt to leave the lagoon but soon find the river blocked by a boulder and several logs. They realize the Gill-Man, as Kay ends up calling the creature has trapped them in the lagoon. They devise a plan to capture the Gill-man by drugging him with Rotenone. They enter the passage way and soon they find a large chamber filled with skeletons of other creatures. Soon they find the Gill-man and drug him, sedating him. Back at the ship they debate what to do when the Gill-man wakes up and on a rampage rips out Pete’s throat and kidnaps Kay, Bringing her to the large chamber of the temple via a cave. David and Carl then follow suit.
Meanwhile, Kay wakes up and tries to escape when she spots the Gill-Man alone mourning over a bunch of skeletons. Realizing that the Creature is a being that can feel Emotions she convinces david and Carl to not kill the creature. The creature, spotting them, threatens them but stands down after they show no harm. They manage to leave the chamber and head back to the ship, and after removing the logs, the lagoon as the Gill-man watches.
In a post credits scene the Gill-man is seen captured by the organization. Meanwhile those left from the expedition are interviewed and they are shown images of other monsters.
- Alfred Molina as Dr. Carl Maia
- Tye Sheridan as Dr. David reed
- Hailee Steinfeld as Kathryn “Kay” Adams
- Paul reiser as Dr. Edwin thompson
- Danny Trejo as Captain lucas
- Rodrigo Santoro as Hector Rodriguez
- Cary Elwes as Richard conroy
- Idris Elba as Pete Meyers
- Doug Jones as The creature/The gill-man