Pokémon : S5 | E1 – Around the Whirlpool

Ash and his friends are on the boat deck discussing their expectations for their adventures in the Whirl Islands. Their ferry soon approaches several large whirlpools, instantly alarming the group. However, two attendants, who are actually Jessie and James in disguise, on the ferry offer them drinks and assure them that it's all right, as they pass through the sea of whirlpools harmlessly. James prepares to net Pikachu, but some turbulence leads him to instead catch Ash. Ash frees himself easily and asks for answers, and Team Rocket promptly reveal themselves. Jessie and James call on Arbok and Weezing to use Poison Sting and Smog, respectively. Ash tries to end the squabble quickly and orders Pikachu to use a Thunderbolt. However, Jessie has Wobbuffet Counter the attack, thereby causing a massive surge that sends Ash’s group and the Rocket trio overboard.

Ash and his friends panic as the ship continues ahead and they are soon being sucked into a whirlpool. Misty calls out Goldeen and Poliwhirl, while Ash gets out Totodile. They start to swim away from the whirlpool, but soon they get dragged in again. The currents suddenly change, and the group realize they are safe. They watch as a mysterious silhouette swims underneath them and hear a peculiar call. A Pokémon comes after them shortly, and Brock realizes it's a Corsola. The Corsola races towards them and circles around them. Soon they are picked up by some tentacles, which they realize is a Tentacruel, and soon taken towards a boat. Misty is enjoying herself, but the others seem quite afraid. The Corsola leaps from the ocean and into the arms of its Trainer, Professor Elm, who happens to be on board.
(Source: Bulbapedia)