Is swimming cardio?

Swimming does work your cardiovascular system and it does use most of the muscles of the body, working your heart. Once again it depends on the amount of energy you put into your swims. On our trips it is likely that your fitness will improve, especially if you are generally a pool or outdoor swimmer that swims less than 2km a day. Lots of our swimmers come back to their clubs or swim groups and find that they can swim with much more stamina and ease than before their SwimTrek trip.