Joshua - Chapter 3
How to Stack a River
The nation camped by the Jordan River in anticipation of crossing into the Holy Land. The people were instructed to follow the Aron (Ark), which would be carried by the Kohanim. They were to keep a distance of 2,000 cubits, about half a mile, to show proper respect but also so that everyone should be able to see the impending miracle.
In order to demonstrate that Yehoshua was a suitable successor to Moshe, G-d performed a miracle similar to one He did when the Jews left Egypt; He split the Jordan River so that the Jews could cross. However, unlike the Red Sea, the Jordan River is a flowing body of water. The rushing water has to go somewhere! Accordingly, the waters upstream piled up vertically into a column.
Given its thematic connection to crossing the Red Sea, Joshua chapter 3 is part of the haftarah for the first day of Pesach. The haftarah continues with excerpts from chapters 5 and 6.