This article is from the Mountain Biking FAQ, by Vincent Cheng.
-Never ride into something that you can't see the bottom of.
-If there are not too many obstacles, you can ride through the water as
usual.
-Instead of cranking in a high gear, try spinning in a low gear if the
water is too deep.
-If the water is real deep, try ratcheting your pedals by doing quarter
pedal strokes.
-Brakes will be much less effective when wet, so watch out.
-Water can get into bearings and damage them. So don't ride things that
are too deep (anything higher than your bottom bracket is considered
deep by most people).
-After riding through the water, pulse both brakes a few times to scrub
off the water.
 
Continue to: