The Pokémon Peninsula > Episode Guide > Episode 7: "The Water Flowers of Cerulean City"

Excited about winning his Boulder Badge, Ash can't wait to get to Cerulean City to battle for his Cascade Badge. For some reason, though, Misty is trying to avoid Cerulean, and leaves Ash and Brock as they enter the city.

When they get to the gym, they find three sisters performing underwater. Ash confronts the girls backstage, finds out that they are the Gym Leaders and challenge them to a battle. The girls (Lily, Daisy and Violet) explain that their Pokémon are too tired to battle, and offer Ash the badge without a battle. Ash is about to take it, when Misty appears and challenges him.

It turns out that Misty is the youngest of the "Sensational Sisters" - also known as "the runt" who said she wouldn't come back to Cerulean until she was a great Pokémon trainer. Ash battles Misty (who's coming out on top) but suddenly Team Rocket turns up with a huge modified vacuum cleaner. They suck the water out of Cerulean's pool, taking all the Pokémon with it. Ash helps the girls save all their precious Pokémon, and gains the Cascade badge for his assistance.