"So when the people broke camp to cross the Jordan, the priests carrying the ark of the covenant went ahead of them." NIV translation
We see that the people decided to follow God's plan for them as they broke camp and followed after the ark of the covenant. We see that they did it the way God had said in that they did not run on ahead and try to cross the river. That is a good lesson for us, as Christians, because sometimes we tend to run off ahead of the Lord instead of taking each step as He directs.
"Now the Jordan is at flood stage all during harvest. Yet as soon as the priests who carried the ark reached the Jordan and their feet touched the waters edge, the water from upstream stopped flowing. It piled up in a heap a great distance away, at a town called Adam in the vicinity of Zarethan, while the water flowing down to the Sea of the Arabah (that is, the Dead Sea) was completely cut off. So the people crossed over opposite Jericho." NIV translation
Because of Spring rains and the melting of the winter snow, the Jordan River was at flood levels. Although the exact location of the town of Adam is not known, it is interesting to note the name which means "man". The Jordan River flows from the Sea of Galilee (peace) to the Dead Sea which is known as such because of its abundance of salt which prohibits much life from living in it.
This river symbolizes man's efforts to find a way to restore their relationship with God (peace). We see that only through God's intervention was the water backed up at Adam and it is a reminder that our only way of salvation (the promised land) is through Jesus Christ.
They crossed opposite of Jericho which was a major oasis in the surrounding desert.
"The priests who carried the ark of the covenant of the Lord stopped in the middle of the Jordan and stood on dry ground, while all Israel passed by until the whole nation had completed the crossing on dry ground." NIV translation
The ark of the covenant, which was the presence of God, stopped in the middle of the river while all of the people passed by. It is interesting to note that prior to this they were not allowed close to the ark. But, after their step of faith into the river, they were able to pass by the ark.