Because sometimes, you get way above your running weight. Anybody in masters swimming? I started about a year ago, and was pretty cynical about my ability to stick with it. I thought it would be too boring. But in reality, its been pretty great. I didn't swim in high school or college, and I am only swimming about three times a week, trying to get it up to four or five, but its (for me) a killer one-hour workout. I am also alot more into the almost mantra quality of swimming -- before it bored me, but now, its kind of neat. And you can go from mantra to speed weight mode by just turning it up a notch. Its always good to get wet and almost nekkid in any case.
I swam at the local YMCA last summer, use to do a mile per day. But now I can find neither time nor a pool to swim. Now I'm all weak and fat, hopefully I can get back into the pool next year. What kept me going fast in the pool often was the person swimming behind me. There was a girl who obviously swims competitively swam in my lane. She often got so close behind me I thought she was going to bite my ankles off.
I used to be a swimmer between when I played soccer. Anybody wanna compare times and see if their as good as a 13 year old? haha. We used to have killer work outs...4X700's (swim, kick, drill, swim) (a 700 would be 28 laps) then our main set was a 3,000 (120 laps)....not an easy thing. I believe the 3,000 was about 50 minutes continious swim.