That hike could very well be the cause of the gain...your body was hanging on for dear life! :-)
Most definitely agree with Karen. Body was under stress from the hike so it was holding on to water to replenish itself. Congrats on completing what sounds like an amazing hike!
Good on ya for trying new things! A few more hikes like that and the Sears Tower is gonna be NOTHING. ;)
ALAN that is sooo amazing about you completing that hike! good for you! pushing yourself outside of your comfort zone is what is going to give you great results. way to go!
Congratulations on your first ever hike, I'm proud of you! My son loves his CamelBak too, I'm old-fashioned and just stop really often to drink water.