University of Florida competitive swimmer Haley Keller completes a tough swim meet, frustrated that she finished second by just a fraction of a second. Shortly after, her sister Beth calls in a panic, warning that Category 5 Hurricane Wendy is barreling toward Florida. Beth has been unable to contact their father Dave, who lives alone in Coral Lake. Despite strict police roadblocks and evacuation orders, Haley drives directly into the evacuation zone to ensure Dave is safe. Haley arrives at Dave's condo in Tampa, but he is not there. Finding their family dog, a terrier mix named Sugar, Haley follows a hunch and drives further inland to their childhood home in Coral Lake, which Dave has been preparing to sell. The town is nearly abandoned, with the hurricane already tearing down trees and overflowing nearby canals. Inside the house, Sugar barks frantically at the open door leading down into the muddy crawl space beneath the foundation. Haley crawls through the dark, damp space beneath the house, navigating support beams and sewer pipes. She finds Dave unconscious with a severe shoulder wound and a broken leg. As Haley attempts to drag Dave toward the exit stairs, a giant alligator emerges from the shadows and lunges at them. Haley manages to pull Dave behind a set of narrow pipes that the massive reptile cannot squeeze through, but the beast blocks the only ladder leading back up into the kitchen. As the hurricane intensifies, floodwater pours through the foundation vents, filling the crawl space. Haley spots her dropped phone near an exterior ventilation grate. When she crawls over to retrieve it, a second giant alligator attacks, crushing the phone in its jaws. Across the flooded street, Haley sees three looters robbing an abandoned gas station. She flashes a flashlight through the grate to signal for help, but the looters are ambushed and torn apart one by one by alligators swimming through the flooded street. Police officer Wayne, who is Beth's ex-boyfriend, arrives with his partner Pete to check the property. Haley screams through the floorboards to alert Wayne. Pete is mauled to death in the driveway, and Wayne enters the crawl space only to be dragged underwater and killed before Haley's eyes. Realizing that the water level will reach the ceiling within minutes, Dave encourages Haley to use her competitive swimming skills. Dave reminds her of the coaching mantra he taught her as a child: Haley is an apex predator who can swim faster than anything in the water. Haley navigates through a flooded sewer drain into the storm-drenched yard, distracting the alligators while Dave uses a shovel to smash through the floorboards above, escaping into the living room. Haley fights off an alligator in the yard and reunites with Dave and Sugar inside the house. However, the hurricane eyewall passes, and the storm surge breaks a nearby levee, sending a tidal wave crashing through the house. The flood sweeps Haley, Dave, and Sugar through the upper floor and onto the roof. During the final struggle, an alligator clamps its jaws onto Haley's arm, dragging her into a violent death roll beneath the water. Using a hand flare she salvaged from Wayne's emergency kit, Haley thrusts the burning flare into the alligator's eye, forcing it to release her. Haley breaks the surface and climbs onto the roof just as Dave and Sugar pull her up. With the storm beginning to clear, Haley lights a second rescue flare, waving it into the sky as a Coast Guard rescue helicopter approaches.

The ending of Crawl brings Haley's emotional and physical journey full circle. Throughout the film, Haley has doubted herself, carrying the lingering pain of her parents' divorce and blaming her rigorous swimming schedule for driving her family apart. Her father Dave spent years pushing her to be faster and tougher, calling her an apex predator who never gives up in the water. During the climactic flood, Haley faces her worst fear. When an alligator traps her in a death roll, she refuses to panic or surrender. By remembering her father's training and relying on her speed and stamina, she turns the tables on the beast and survives an attack that would kill almost anyone else. When Haley, Dave, and Sugar finally stand together on the roof of their destroyed home, the hurricane clouds begin to part. Haley holds the bright red rescue flare high above her head as a helicopter flies into view. The survival ordeal has reconciled father and daughter, restoring Dave's will to live and validating Haley's strength. The closing song, Bill Withers' classic "See You Later, Alligator", plays over the credits, offering a fun and triumphant punctuation mark to an exhausting battle for survival.