Walking is good to stay fit, power walking is better. Knowing is one thing changing your life style to do it is another. Running, if you are still young enough to learn, is best but its impact on your body is 3 times as large than walking.
I could swim when I was young. I remember ever since I learned the basics I could swim up to a kilometer continuously almost. At beaches I could swim back and forth the pontoon (floating platform) a few times.
Really I can’t recall for how many years I have not seriously swam in an Olympic pool, perhaps 25 or more!
I have recently joined a recreation club near to my office. My plan was to swim for half an hour during lunch time twice every week instead of running in the morning. It’s really too hot in summer to run even at 6:30am in the morning.
200 meters was the best I could do this week, poor me, very disappointing!