The Eisch is a river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 flowing through Belgium

Belgium

Belgium , officially the Kingdom of Belgium, is a federal state in Western Europe. It is a founding member of the European Union and hosts the EU's headquarters, and those of several other major international organisations such as NATO.Belgium is also a member of, or affiliated to, many...

 and Luxembourg

Luxembourg

Luxembourg , officially the Grand Duchy of Luxembourg , is a landlocked country in western Europe, bordered by Belgium, France, and Germany. It has two principal regions: the Oesling in the North as part of the Ardennes massif, and the Gutland in the south...

, joining the Alzette

Alzette

The Alzette is a river with a length of 73 kilometers in France and Luxembourg. It is a right tributary of the Sauer.It rises in Thil near the town Villerupt in the Meurthe-et-Moselle département, France. It crosses the border with Luxembourg after a few kilometres. In Lameschmillen it is joined...

 on its left in Mersch

Mersch

Mersch is a commune and town in central Luxembourg, capital of the canton of Mersch. It is situated at the confluence of the rivers Alzette, Mamer and Eisch., the town of Mersch, which lies in the centre of the commune, has a population of 3,345...

. It flows through the towns of Eischen

Eischen

Eischen is the largest town in the commune of Hobscheid in south-western Luxembourg, and its administrative centre. As of 2005, the town has a population of 1,532.-Name:...

, Hobscheid

Hobscheid

Hobscheid is a commune and town in western Luxembourg. It is part of the canton of Capellen, which is part of the district of Luxembourg. The commune's administrative centre is Eischen....

, Septfontaines

Septfontaines

Septfontaines is a commune and small town in western Luxembourg. It is part of the canton of Capellen, which is part of the district of Luxembourg. , the town of Septfontaines, which lies in the centre of the commune, has a population of 356...

, and Marienthal

Marienthal, Luxembourg

Marienthal is a village in the commune of Tuntange, in western Luxembourg. , the village has a population of 105. It is known for the former monastery Marienthal, of which a few buildings remain....

.

It has several sources near the villages of Sélange (Belgium) and Clemency

Clemency, Luxembourg

Clemency is a commune and town in south-western Luxembourg. It is part of the canton of Capellen, which is part of the district of Luxembourg....

 (Luxembourg).

The Luxembourgian part of the Eisch is informally known as the 'Valley of the Seven Castles

Valley of the Seven Castles

'Valley of the Seven Castles' is an informal name given to the Eisch valley, in central Luxembourg. The valley stretches from the confluence with the Alzette upstream to Steinfort, on the border with Belgium. The entire route can be traversed in about an hour by car, starting near the town of...

', for the seven castles that line its route.