The Emscher (German pronunciation: [ˈɛmʃɐ] ⓘ) is a river, a tributary of the Rhine, that flows through the Ruhr area in North Rhine-Westphalia in western Germany.

Towns along the Emscher are Dortmund, Castrop-Rauxel, Herne, Recklinghausen, Gelsenkirchen, Essen, Bottrop, Oberhausen and Dinslaken, where it flows into the Rhine.

At the centre of a vast industrial area with 5 million inhabitants the river is biologically dead, as it was used as an open waste-water canal from the end of the 19th century.

The subsidence caused by coal mining along its route made the option of subterranean sewer pipes running alongside unworkable, as they would break each time the ground shifted.

Owing to the steady flow of spoil from the mining industry it has been impossible for the route of the Emscher to be maintained and its mouth into the Rhine has shifted north twice.