"The Jordan River will turn back. But what is the value of the Jordan, and what does it matter to him? Were people standing in the Jordan? Rather, we learn from here that if the leader flees, all will flee. Once the Jordan saw that the Sea had fled, it too fled. Moses said to the Sea, 'You did not say, "I will not split," yet now you are fleeing? What is it to you, Sea, that you flee?' The Sea replied, 'I am not fleeing from you, but from the Master of the Universe, who instructed the dry land to emerge from me on the third day of Creation, whereas you were created on the sixth day. I am not fleeing from you, Moses, but from Jacob's God, the Rock who transforms a desert into a water spring.'"
When the Jordan River Parted for Joshua and Israel
Midrash Tehillim 114:5