Is it fat or muscle weight gain

I have been semi-stalled for a month and just increased three pounds. I have just got into bicycling with an average of 20 miles a day. Do you think the high level of excercise can contribute to the stall or gain. Is it possible muscle building or should I be concerned.

You're probably just looking at day to day variations in your weight.  From my experience, high levels of exercise does help build muscle, and muscle is more dense than fat, but unless you have really upped your calories or carbs, you won't be adding weight.

In the long run, all that muscle will speed your weight loss, so keep up the exercising!

Muscle is denser than fat, but in this situation you might have to monitor how your clothing fits to make sure that you are not gaining fat. Bicyclists are generally thin but have dense muscles. 

 Starting a new exercise program DOES cause a slight weight gain in the beginning, and it's neither fat nor muscle - it's water.  The new muscles that you are working in a different way fill with water.  It'll even itself out and you'll start to see results once you stick with it for a little while.

Water.  You would have had to eat an extra 10500 calories at least to gain 3 lbs. 

 Like others the likely culprit is water.  

 we do tend to fluctuate day to day,