weight loss

Hey Everyone! I've noticed that it was so much easier to loose weight with running, as opposed to swimming. It seems even though i'm swimming hard, the 13 or so pounds that I need to loose haven't budged. When I was running, my diet didn't have to be really clean...in fact I ate pizza at least once a week, and found that it helped me during high mileage. During running, my weight was very low despite the pizza habit. While swimming makes me hungrier, and I'm probably burning more calories per workout, the weight loss isn't there. Why is this? Thanks, Jerrycat