
In the opening scene, Scrat, the saber-toothed squirrel climbs a glacier and comically zips away as he spits out gallons of water, after gnawing a hole in the ice. With their first meal, the two reptiles swam away.

At that moment, however, Stu is pulled under the surface and consumed by the sea reptiles, his shell regurgitated from the waters in front of Fast Tony, who, unfazed by the demise of his assistant, attempted to pawn the empty shell off to other creatures. James had stayed back at the waterpark, blowing bubbles into the waters before he was frightened off by Stu, who went swimming with the use of one of the river reeds he and Fast Tony were peddling. The herds of animals move along towards the end of the valley, with Manny moving everyone along before Sid offhandedly remarks that Manny is going extinct, a rumor aided by the aardvark that stated that mammoths were extinct, which he announced to his children, one of whom went missing: a young aardvark named James. Within the ice, unseen by the animals, are two frozen sea reptiles named Cretaceous and Maelstrom.

Manny then ushers the animals along and takes a moment to look out at the chunk of broken ice in the lake suspiciously, until Diego moves him along as well. The vulture then explains his intent to eat those that die off in the flood before flying off, and with that a large chunk of ice breaks from the glacier forming the waterpark, nearly crushing some of the animals on the slides before landing in the meltwater lake. At that moment, however, a vulture known as the Lone Gunslinger appears and states that the valley will flood over, with the only means of escape being a boat at the end of the valley, which they must reach before three days, when the waters hit the geyser fields near the boat. Moving back to warn the other animals, Manny, Sid and Diego slide down the Eviscerator and nearly collide with Fast Tony, whose lies they confirm as true, to the skepticism of the other animals. As Manny and Diego go up to get him down, they see that Fast Tony's claims were correct: behind the walls of ice is a vast body of meltwater. Manny discredits this, stating that the world will not flood over, when one aardvark discredits his ideals, claiming that Manny is the last mammoth, when attention shifts to Sid, who is standing atop the Eviscerator, the tallest water slide in the park, with the intention of jumping. Manny and Diego move on to find that Fast Tony, a local armadillo con artist, with the help of his assistant Stu, is attempting to convince the other animals to buy river reeds from him, claiming that the the world will soon flood over and that by purchasing his products they might survive. None take the sloth seriously, to his dismay, and Sid wanders off to find another means of earning respect. Manny, Sid and Diego are among the animals at the waterpark, with Sid attempting to earn respect from his peers by starting up a day camp for young animals.


Two months after the events of the first film, Scrat the saber-tooth squirrel tries to access his acorn, which is lodged into a great wall of ice, but releases a stream of meltwater from the ice wall upon removing the nut, which blasts him down into an ice slide where a young platybelodon slides down, carrying him along, as the young animal reaches a vast waterpark where herds of other animals are all enjoying the pools and slides formed from the melting ice.
