The IJssel was the lower part of the small river Oude IJssel. The river was a natural line of defence in 1945 04, called Oude IJssel. The current Oude IJssel is until today the second-largest contributor to the flow of the river. The source of the Oude IJssel is in North Rhine-Westphalia near Borken. The average discharge has been stated per second as 300 cubic meters. Various tributaries add sometimes as Schipbeek streams and the Berkel a considerable volume of water to the total flow of the IJssel.
The IJssel river is the only branch of the Rhine delta. The area had been prone in times of northwestern gale s to flooding. Another branch had silted already completely up by the middle of the nineteenth century.
Aachen is the westernmost city, the administrative centre