My horse tries to jump small creeks or if we are going down a very steep bank then heading back up the other side he'll try to jump the last little but onto the upper bank. Not my favorite. He does however, slog through mud no problem. I keep his chin tucked so he can't reach out to jump and we ease our way into whatever he wants to jump. Then I let up just a little so he doesn't jump out of it. It only takes me doing this one time per ride and he knows that I won't let him jump.
Riding: The art of keeping a horse between you and the ground. ~Author Unknown