I agree swimming is a really good sport to improve your lung function. I swim to releive stress and also to fill my weekly cardio workout routine. I prefer swimming instead of jogging becuase jogging puts pressure on your legs, at the end your day your legs get sore, but when I swim I use 4 diffrent strokes freestyle, butterfly, backstroke, and breaststroke. These 4 strokes workout my whole body and at the end of the day my whole body is sore.
I agree and this is actually why people who are extremely overweight are advised to do exercises in a pool first as they get their weight down to an amount where if they jog they won't be putting too much stress on their legs and joints anymore. What I also like about swimming a lot better than most other exercises is that you get more a bit more workout in terms of being able to exercises your whole body as compared to just your legs when you jog for the same amount of time.