The Emscher is a relatively small river and tributary of the Rhine, flowing through the Ruhr area in North Rhine-Westphalia in western Germany. Its total length is 84 km with an average discharge near the mouth into the lower Rhine of 16 m³/s (cubic metres per second).
The Emscher has its source in Holzwickede, east of the city of Dortmund, and flows west through the Ruhr area. Towns along the Emscher include Dortmund, Castrop-Rauxel, Herne, Recklinghausen, Gelsenkirchen, Essen, Bottrop, Oberhausen and Dinslaken, where it flows into the Rhine.
In the geographical centre of a vast industrial area of 5 million inhabitants, the river is biologically dead, as it was used as an open waste water canal since the end of the 19th century. Massive mining subsidences from the many coal mines in the Emscher's course had made parallel subterranean sewer pipes unfeasible as they would break too easily.
Due to the continual down river movement of soil from the mining industry, it has been impossible for the natural course of the river to be maintained, and consequently its mouth into the Rhine has been relocated north twice. A huge modern sewage treatment plant at its mouth ensures that the water of the Emscher enters the Rhine in an acceptable quality.
Since the early 1990s, a huge renaturation project for the Emscher river has been progressing. To fully rehabilitate the river, a large subterranean pipe is - now that coal mining in the river's course has ceased save one mine in Bottrop - currently being constructed along the course of the river. The first section of the river subject to renaturation is in the city of Dortmund. The total project is managed by the public water board Emschergenossenschaft. The financial frame is 4.5 billion Euro and the aim is to finish the main work by the year 2020.