I really enjoy swimming in the summer. DO you?
Yes, I do enjoy swimming, which is self-propulsion through water.
I see, is it a good activity to lose calories? 
Sure, many people like to swim for exercise. You can do different strokes and vary the amount of exertion required.
Sounds interesting, do you swim in the ocean?
Yes, I have. The salt water provides more buoyancy which makes it a little easier to swim.