I know it does. But for reasons I don't understand, I don't lose weight doing it.

I started swimming after I got a stress fracture in my foot from running. Actually I've been swimming off and on for years.

What I've noticed is that compared to periods when I run a lot (for me, running 18 miles/week is a lot) swimming doesn't make me lose weight. My usual swim routine BTW is just to get in the pool and swim for a mile, taking as few breaks as I can. I can swim a mile in about 33 minutes.