Actually, you do sweat quite a bit when swimming but you just don't realize it. Swimming is great exercise and many people prefer it because it is a non-impact activity, whereas running sometimes leads to leg injuries. In my experience (I was a competitive triathlete years ago), running is more effective in terms of getting the most bang for your buck, but swimming isn't bad, either. One problem with swimming for many people is that poor technique often leads quickly to fatigue. We all learn how to run with correct form (well, most of us
), but most people never learn good swimming technique unless they swim competitively. Hope this helps.