Most rivers follow a course that takes many turns, but the nature of the terrain typically involves a series of alternate left and right turns. Many rivers even meander, which means that their course is a succession of left and right turns, to the point where each curve looks like a horseshoe.
Instinctively, it would look a bit odd to find a river whose turns are more pronounced on one side than the other. This would mean that its course is shaped like a spiral. This is exactly how the upper course of the Blue Nile goes. On this map, one can see that it makes a full 180 degrees right turn before reaching Lake Tana in the Ethiopian highlands, and then goes on to make a full 360 degrees to the right, until it veers right and follows a more classic course all the way to its confluence with the White Nile in Sudan.
We don't know of other 540 degree spirals in the world, but chances are that others exist.
The Blue Nile
