new exercise routine - retaining water??

fortally

I joined MFP just after the new year and began exercising again. Just 20-30 min. every other day or (sometimes skipped 2 days, depending on soreness). I started with treadmill "brisk" walking and workout dvds (mainly Biggest Loser, level 1 only). I did that for 2 1/2 weeks and lost four pounds. This last week I've noticed my endurance improving and I was able to increase the workouts to almost every day. On cardio days I'm up to 45 min (either treadmill - "brisk" walks with some jogging & sprints - or step aerobics) and on dvd/sculpt days I can now do 2 levels without all the soreness. However - the weight loss stopped at the same time I upped the workouts. I haven't gained - I'm just seeing the same number over & over on the scale.

My diet hasn't changed. I'm fanatical about weighing/measuring food and tracking calories, so I'm fairly certain I'm eating at a deficit (eating back exercise calories & netting 1200/day). I really don't think overeating is causing the weight loss stall.

My question is - can increased exercise cause you to retain more water? I read that your body hangs on to water for muscle repair, and I'm wondering if this is why I'm stalled out on the scale? The initial weight loss couldn't have been all water because my jeans are definitely looser (no longer have to suck it in & pray to get them zipped!). I'm wondering if I have in fact burned off some fat, but my body is just hanging on to fluids (so the scale looks the same)?

Just curious about the relationship between increased exercise and the scale. I'd love to hear feedback and if anyone else has noticed this?