"Where are you swimming?"
yes, this is my question also. Gdzie Ty pływasz? to me says Where do you swim? and Gdzie płyniesz? asks Where are you swimming to? - They are two different questions. I do understand that one might use dokąd for the second - but still I would suggest that Gdzie Ty pływasz? is an alternative correct response. I have never studied Polish grammar - I'm just a native (out of country) speaker. I go by what sounds right - happy to be corrected. I am loving this course!