I want to be the worlds best swimmer!
You must be good at holding your breath under water then!
I feel like I am! Why... Is that a prerequisite?
Well you need to be able to hold your breathe while stroking! But good for you, I mean swimming is one of the lower impact sports out there! 
So I've heard!
Well, as a formalized sport, swimming features in a range of local, national, and international competitions, including every modern summer Olympics. Have you competed in any of these levels?