The male protagonist doesn't know how to swim, but the female protagonist does, and from the way she swims, it's obvious how much she loves it. Throw in a coach that is a random person not a teacher from the school and this is what you get.

Our hero who doesn't know how to swim joins his school swimming club and begins to learn from their star swimmer who loves swimming more than anything. Good thing she's cute and nice to boot!
Russian / Русский