God dried up the Jordan River when the priests were obedient to put their feet in the water. The Bible says that when their feet were "dipped in the brim of the water... that the waters ...rose up in a heap very far from the city Adam, that is beside Zaretan." Not only did the waters which were at flood stage recede, the ground that the Israelites walked on was dry.
God not only cleared their way, He made it so they wouldn't have to slog through mud and get bogged down going through the Jordan. But first, He told them they needed to spend time in preparation, sanctifying (set apart, free from sin/purify) themselves to the Lord.
Once the Israelites crossed the Jordan the Lord had them bring twelve stones out of the Jordan to set up as a memorial to what He, God, had done for the people. Twelve stones were also set up in the middle of the Jordan as a reminder.
God gave specific directions for a task that at best could have been very uncomfortable to the Israelites, but once they obeyed, God provided a perfect path for them to walk. An example for me to remember and follow.
Check out this link with photos of Israel: http://www.experienceisrael.com/index.php?option=com_content&task=section&id=7&Itemid=117