No wonder we find Greek problematic. Round our way "Πάω/πάμε για μπάνιο" ή "Πάω/πάμε κολύμπι" seems to mean, roughly, "I'm going/let's go for a dip" which generally turns out to be, swim a few strokes, meet ½dozen friends, form a 5m circle in chest deep water and chat while occasionally dipping down to shoulder depth. Occasionally swim a few more strokes. Repeat until hungry/thirsty.
A Greek friend's son, on the other hand, is a serious swimmer. He goes to coaching sessions at a pool. Κολυμπάει