Pokémon S02 E29 The Wacky Watcher!

"Gotta catch 'em all!"

On Rind Island, Tracey meets Dr. Quackenpoker, a noted Pokémon Watcher who is doing a study on the Magikarp that climb up waterfalls and how they evolve into Gyarados. However, Team Rocket appears to steal the Magikarp and get them to evolve.