The Ourthe (Walloon: Aiwe d' Oûte) is a 165-kilometre (103 mi) long river in the Ardennes in Wallonia (Belgium). It is a right tributary to the river Meuse. The Ourthe is formed at the confluence of the Ourthe Occidentale (Western Ourthe) and the Ourthe Orientale (Eastern Ourthe), west of Houffalize.
The source of the Ourthe Occidentale is near Libramont-Chevigny, in the Belgian province Luxembourg. The source of the Ourthe Orientale is near Gouvy, also in the Belgian province Luxembourg, close to the border with Luxembourg.
After the confluence of the two Ourthes near Nisramont, the Ourthe flows roughly in north-west and later in northern direction. Near Noiseux it flows for a short distance through the province of Namur. After the municipality of Durbuy it flows in the province of Liège. Eventually it flows into the river Meuse in the city of Liège. The most important tributaries of the river Ourthe are the Amblève and the Vesdre. Towns along the Ourthe are Houffalize (Ourthe Orientale), La Roche-en-Ardenne, Hotton, Durbuy, Hamoir and Esneux.
Coordinates: 50°07′44″N 5°40′38″E / 50.1288°N 5.6773°E