The Roer (Dutch: [ruːr] ⓘ, Limburgish: [ʀuːʀ˦]) or Rur (German: [ʁuːɐ̯] ⓘ; French: Rour[2] [ʁuʁ]) is a major river that flows through portions of Belgium, Germany and the Netherlands.

A fortified area known as the Roer Triangle, formed by the towns of Roermond and Sittard, in the Netherlands, and Heinsberg in Germany, was the scene of heavy fighting at the beginning of 1945.

Between 16 December 1944 and 23 February 1945, the U.S. Ninth Army was unable to advance across the Roer during Operation Queen, because German forces controlled dams close to the river's source in the densely forested region of the Hohes Venn.

At the same time, the German Ardennes Offensive meant any further westward push would leave Allied forces stretched and supply lines exposed.

As the flood waters began to subside, Allied forces crossed the Rur in rafts in the early hours of February 23, 1945, as part of Operation Grenade.

The towns along the Roer are Monschau, Heimbach, Nideggen, Düren, Jülich, Linnich, Hückelhoven, Heinsberg (all in Germany) and Roermond (Netherlands).

The upper section above the Roer reservoir (German: Rurtalsperre Schwammenauel) offers 20 kilometres (12 mi) of white water ranging from class III(+) to I.