Stepping out of the water and back onto solid ground, a sudden and miraculous transformation of the landscape reveals itself. As the angel brings the prophet back to the dry land, a completely new sight appears. Right along the edges of the stream, a massive number of trees have suddenly grown.
The primary approach among commentators is that this event is one of rapid, miraculous creation. In the brief period it took for the angel to lead the prophet through the water and return him to the shore, an abundance of trees managed to sprout and flourish. This is a completely new development, as these trees were not there at all before the prophet first stepped into the water [רד״ק]. Now, this wondrous new growth lines both sides of the stream.