The Ruhr (German) or Roer (Dutch) is a major river that flows through portions of Belgium, Germany, and the Netherlands. It is a right (eastern) tributary to the Meuse (Meuse / Maas). About 90 percent of the river’s course is in Germany.
It is not to be confused with the rivers Ruhr and Röhr, which are tributaries of the Rhine in North Rhine-Westphalia.