Quote Originally Posted by Dogmama View Post
I hope so. I've been doing my 40 laps X 25 yard pool and man - it's tough! I get a 30 second rest at each side so the whole thing takes less than an hour and I'm totaled! What a water-weanie I am. I could bike full-out for the same amount of time and be LESS spent.
VERY common for swimming! I always feel more tired (and hungry) after swimming.

Your brain is also working hard, which makes you more tired. It gets more autopilot the less you have to think. When I was taking lessons a couple of years ago (and this was before my second or third Ironman, so I'm not new to swimming) I was WAY more tired on lessons where the instructor tried to adjust my form and I really had to think about what I'm doing every step of the way.