Plot
In Aroostook County, Maine, Department of Inland Fisheries & Wildlife officer Walt Lawson is scuba diving in Black Lake, supervised by Sheriff Hank Keough. The officer is suddenly attacked underwater, and bitten in half by an unknown creature.
United States Fish and Wildlife Service officer Jack Wells, American Museum of Natural History paleontologist Kelly Scott, and Hank decide to investigate the incident. They are joined by Hector Cyr, a wealthy mythology professor and crocodile enthusiast, who suspects the culprit to be a freshwater crocodile much to the disbelief of the group.
During the group's excursion on the lake to locate the creature, Kelly and Hank's canoe is flipped over, including the discovery of a severed human toe and a moose head. Hank's deputy Burke is killed when his head is bitten off, which confirms Hector's suspicions, although Hank remains skeptical. That evening, the group make camp, and prepare a plan to capture the creature.
The next day, as Hank and Hector get into an altercation, a large grizzly bear ambushes them, when a gigantic 32 ft (9.8 m) long saltwater crocodile suddenly emerges from the lake, and drags the bear away. The group discover local resident Delores Bickerman, an elderly widow living near the lake, feeding a blindfolded dairy cow to a nearby crocodile. She reveals that she had been feeding it for years, after the crocodile devoured her husband.
Hector, and Deputy Sharon Gare take a helicopter onto the lake to separately locate the crocodile by landing in its territory. While scuba diving, Hector is confronted, but he and Gare escape by distracting it with an inflatable raft. Hank and Jack call in the Florida Fish and Wildlife Conservation Commission to help capture and kill the crocodile. Hector suggests luring it out of the water and tranquilizing it instead. Jack reluctantly accepts the proposal, and they use one of Bickerman's cattle dangled from the helicopter as bait.
By nightfall, the team assembles on the lakeshore to track down and capture the crocodile. It reveals itself by attacking Hector's helicopter. Hector pulls up when the crocodile lunges, and Jack fires a tranquilizer dart into its neck with a clear shot. Hector loses control, and crashes yards offshore. The crocodile then comes on land, and pursues the team. During the skirmish, Kelly is knocked into the lake by the crocodile's tail, and manages to swim towards the downed helicopter, before the crocodile catches up. It becomes trapped as it tries to attack Hector and Kelly, before seemingly neutralized by the tranquilizer.
Jack, Hector, and Hank argue about whether to kill the beast or not. Jack eventually grabs Hank's gun and shoots it, but the firearm turns out to be another tranquilizer. As Hector and Kelly emerge out of the water, another crocodile appears, but Hank blows it up with a grenade launcher. Soon after, Florida wildlife officers arrive to take the crocodile away to Portland, Maine, deciding what to do next with it.
One week later, Bickerman is feeding bread crumbs to many baby crocodiles, revealing the two adult crocodiles were actually a mating pair. The only surviving crocodile is seen tied to the back of a flatbed trailer travelling down the highway.
