Just to add to the chorus - it's definitely the case for me too. I lift heavy and hard, and I can retain 3-4 pounds of fluid a day after a workout. Drives me crazy!
I slacked off going to the gym for about 4 weeks as I got overwhelmed with work for a bit - it was quite funny to see my wild weight fluctuations stabilize. That post-workout fluid retention was the single biggest contributor to my daily weight swings! As soon as I went back to the gym, the wild swings came back.