If you go to swim in a swimming pool, you probably need to share a track with others. You have two ways to share. You may suggest to another person: "Shall we half-half, or circle?" By the way, if somebody else is already in and you just arrive, you may ask: "Can I go?"
We Chinese like to describe somebody as a "Han Ya Zi". I don't know how to translate it into English. For the similar meanings, however, we can say "Sailor is no swimmer". I am just kidding---Sailor is very good at swimming.