I love summer.  This time of year is a perfect time to go swimming.
Swimming? The self-propulsion of a person through fresh or salt water, usually for recreation, sport, exercise, or survival? I love it! 
Swimming is one of the best workouts you can do.  It works all of your body, gets the heart rate up, and it is very low impact!
And swimming is low-impact compared to land activities such as running.