Pokémon : S3 | E16 – For Crying Out Loud

Brock looks through his guidebook and informs Ash that they should head to Azalea Town for the next Gym. The trio soon stops to admire a scenic lakeside town, where Brock spots a girl at a cliff. Misty also spots a Marill and attempts to catch it. However, the Poké Ball simply hits Marill on the head, causing it to cry out loud. As Brock comforts the Marill. Ash notices the pink bow on her tail and points out that she must already have a Trainer. Misty tries to hold her, but Marill doesn't seem to like her and cries again.

Team Rocket appears, disguised as farmers, and they offer to give the group a lift. Unaware of the plot, Ash and his friends hop on the vehicle. Just then, two hands appear from the hay and grab hold of Pikachu and Marill. Team Rocket detaches the vehicle's tray and flees, leaving Ash, Misty, and Brock behind. Ash and his friends give chase as Team Rocket recites their motto. Marill lets out an ear-splitting cry, causing Meowth to lose control of the truck and crashes it into a railing, sending Team Rocket blasting off. Pikachu and Marill roll down the hill towards the riverside. Ash tries to go after them but lands on a tree. Brock stays behind and keeps Togepi safe, while Misty continues down the hill and grabs the two Pokémon. Unfortunately, she is unable to stop and falls into the river. Ash and Brock watch as Misty, with Pikachu and Marill in hand, is washed downstream.
(Source: Bulbapedia)