The river Moselle enters the Rhine at the German town of Koblenz. The Moselle is the most important waterway in the Rhine catchment area after the Rhine itself. It is the largest tributary of the Rhine after the Aare.
The Saar is the largest tributary of the Moselle.
Another tributary of the Moselle is the Sûre (also called Sauer). This river flows through Belgium, Luxembourg and Germany. Between Wallendorf and Wasserbillig the Sûre is a condominium, which means that the entire width of the river belongs to two countries, in this case Germany and Luxembourg. The Moselle itself is also a condominium on the border between Germany and Luxembourg.