In the North Atlantic off the coast of Greenland, a highly advanced deep sea oil rig has been recently constructed by the company Nexecon Petroleum, and named "Colossus" for its immense size. This "new" type of oil rig can dig deeper and extract more oil than any other in the world. The fact that this huge rig has been built on fault lines alarms geologists, who are concerned that the delicate ocean floor fault lines in that region might be disturbed through deep drilling, with catastrophic consequences. A reporter, Christen Giddings, has been invited by the CEO of Nexecon, Peter Brazier, to the oil rig in an attempt to address the concerns of the geologists. Christen is accompanied by a trusted cameraman Jake Thompson, who will record their findings. The oil rig's crew seem to be convinced that nothing bad will happen, and are skeptical of the geologists. Brazier hopes that a documented report on "Colossus" will reveal that his rig has all the necessary safety arrangements and that the region is stable enough for a drilling operation. As the drilling commences, a rich oil deposit is discovered. However, further drilling is not stopped and an "ocean floor fault line" gets ruptured, which opens a portal to a "mirror" ocean, hidden under the normal ocean for millions of years and containing prehistoric life. An explosion occurs and the drilling system collapses. A team of engineers descend through a glass elevator to assess the situation. A giant animal is spotted approaching, which turns out to be the most powerful and fearsome oceanic predator that ever lived, Carcharodon megalodon. A struggle for survival ensues as the crew and geologists attempt to escape from "Colossus", during which several people fall victim to the beast. In a desperate move to stop the monster shark, one of the crew members, Ross, lures it to an open space with his small submarine and overloads the fuel tanks of the machine, resulting in a gigantic explosion that kills both him and the beast. The ordeal is not over yet as another Megalodon ventures into open waters, passing below a boat with Christen Giddings on board. However she is unaware of its presence.
A group of friends wakeboarding are attacked and devoured by a two-headed great white shark. Meanwhile, a Semester at Sea ship, called the Sea King, led by Professor Franklin Babish (O'Connell) and his wife, Anne (Electra) hits a dead shark, which becomes lodged in the boat’s propeller and damages the ship's hull, causing the boat to take on water. Soon after, the two-headed shark attacks the boat and breaks the radio antenna, preventing ship co-captain Laura (Thompson) from summoning help. The group then notices a deserted atoll nearby, so Laura drives the Sea King closer, before Professor Babish takes the students over to the atoll on a dinghy, while Anne remains on the Sea King with Laura and the ship's crew, Han (Webb) and Dikilla (Valentin).
While wind surfing near the seaside community of Port Harbor, a young man is killed by a giant Great White Shark. Author Peter Benton and professional shark hunter Ron Hammer realize the truth, but ambitious governor William Wells refuses to accept that a shark threatens their community. Fearing that a canceled wind-surfing regatta would derail his gubernatorial campaign, Wells has shark nets installed. But the sounds of teenagers splashing in the surf leads the shark to rip through the nets. The next day, the shark plows through the wind surfers, knocking them off their boards. But rather than eat the scattered teenagers, the shark targets the governor's aide and eats him.
James Ziegler has spent five years of his life planning the perfect crime, planting covert listening device on the communication devices of influential mega rich businessman Mr Rosentski. His dream finally comes through when he records a sensitive conversation between Rosentski and the President of the United States; so sensitive that he demands $2 million in diamonds from Rosentski for a disc of the recording. The easy going Mr R pays James for the disc but his Public Relations Enforcer bungles an attempt to retrieve the disc, the diamonds and James who escapes with the disc, the diamonds and his life.
Two ocellaris clownfish, Marlin and his wife Coral, admire their new home in the Great Barrier Reef and their clutch of eggs when a barracuda attacks, knocking Marlin unconscious. He wakes up to find that Coral and all but one of the eggs have disappeared. Marlin names this last egg Nemo, a name that Coral liked.
The film takes place along a stretch of coastline somewhere in Florida in the United States, where a local tourist spot has become plagued by a mysterious marine creature. Little do they know, the monster is the product of a secret military experiment — a genetic hybrid mutated from a common octopus and the prehistoric super-predator Dunkleosteus. Unfortunately, the creature has broken loose, and is now feeding on swimmers and tourists swimming or sailing along the coast. Also, the monster is only an infant, and will continue to grow if it is left to hunt much longer.
Mike Di Donato, an Italian-American man with a mysterious past, leads a solitary life in an anonymous sea island. His unusual work is the hunting of sharks, from which his partner derives handicrafts for the local market.
Steven (Hugo Stiglitz), a US-born Mexican businessman, arrives in a Mexican fishing/resort village for a vacation on a yacht anchored off shore. One of the local fishermen, Colorado (Roberto Guzmán), takes Steven with him when he goes to haul in the sharks he has caught. Colorado is annoyed to learn that another shark has taken a huge bite out of one of his captured sharks. Steven says he feels bad for the sharks, then shrugs, "that's life." He then decides to scope to local beaches for sexy women. He sets his sights on Patricia (Fiona Lewis), an Englishwoman on vacation. They have a whirlwind romance but break up when Steven can't decide if he is in love with her. Steven is extremely jealous, however, when she begins a relationship with Miguel (Andrés García) a womanizing swimming instructor at the nearby resort hotel. While Steven stews on the yacht, Patricia and Miguel have sex. Then she goes skinny dipping in the ocean for a morning swim and is eaten by a large, apparently emphysemic, 19-foot-long (5.8 m) tiger shark.
While a group of teenagers are having an evening beach party on Amity Island, Chrissie Watkins (Susan Backlinie) goes skinny dipping in the ocean. Something violently grabs and pulls her underwater. In the morning, Deputy Hendricks (Jeffrey Kramer) finds her remains on the beach. Upon hearing from the medical examiner that the cause of death was a possible shark attack, Police Chief Martin Brody (Roy Scheider) proceeds to close the beaches, but Mayor Larry Vaughn (Murray Hamilton) overrules him, fearing news of a shark attack will ruin the summer tourist season, the town's primary revenue source. He rationalizes that there have been no prior shark problems in the area, and theorizes the girl was killed in a boating accident. The coroner concurs and Brody reluctantly accepts their conclusion.
A great white shark follows a team of water skiers. The driver stalls the ski boat but manages to restart it before the shark can approach. The shark follows the water skiers into the SeaWorld park and throws the gate off its rails while it is closing. Meanwhile, Florida announces the opening of SeaWorld's new glass covered underwater tunnels that allow close up views of the park's animals.
On Amity Island, Chief Martin Brody (Roy Scheider), the hero of two previous shark attacks, has died from a heart attack. His wife, Ellen (Lorraine Gary), attributes it to the fear of sharks. She now lives with Brody's younger and more obedient son Sean (Mitchell Anderson) and his fiancée Tiffany (Mary Smith). Sean works as a police deputy and is sent to clear a log from a buoy a few days before Christmas. A massive 25-foot great white shark attacks him, severing his arm, then pulling him underwater and killing him.
The coastal town of Hampton Bay is threatened when a 35-foot great white shark starts chomping up their vacationers. Days before the annual Regatta celebration, the townspeople are faced with financial ruin if something isn't done about their newfound shark problem. If that wasn't enough, the owners of the local amusement park have been subject to a hostile takeover from a prospective businessman looking to cash in on their prized property. It's then up to the sheriff, the park's owner, and a shark expert to head out and kill the shark before the summer economy is slashed and the park is demolished.
Prior to a new hotel opening on Amity Island, a huge great white shark ambushes two divers who are photographing the wreck of the Orca, the late Quint's boat. A few days later, the shark devours a water skier. The speedboat driver defends herself by dumping gasoline on the shark (accidentally spilling some on herself) and shooting it with a flare gun, causing the boat to explode. The shark escapes but is severely scarred.