Ranma ½, part 7 number 2

Akane can't swim and the principal tells her if she can't learn how to she's not allowed to be promoted to the next grade. Then he volunteers to teach her how to swim. The principal ties a boulder to her back and tells her to jump into a pool into which he has put a shark.

Ranma saves Akane from the shark. The next day the principal tells Akane he's made her a swan outfit. Itr's actually more a form of a mutant big-bird outfit that she has to get inside. It's supposed to work, but it causes her to be upside down in he water instead.

Then he puts a mermaid outfit on her and tries to hold her up with a fishing rod but she still sinks. Then he gives her a life preserver to use. She still can't swim.