Ruhr, Ruhr Valley, Ruhr district... da scheint es im Englischen keinen einheitlichen Begriff zu geben, am gebrauechlichsten ist wohl Ruhr:
Main Entry: Ruhr
Usage: geographical name
1 river 146 miles (235 kilometers) W Germany flowing NW & W to the Rhine
2 industrial district in valley of the Ruhrhttp://www.m-w.com/cgi-bin/dictionary?book=Di...
(rr) (KEY) , region, c.1,300 sq mi (3,370 sq km), W Germany; a principal manufacturing center of Germany and formerly known as one of the worlds greatest industrial complexes.[...]
The Columbia Encyclopedia, Sixth Edition. 2001-05., http://www.bartleby.com/65/ru/Ruhr.html
(ROOR) Valley of the Ruhr River, in west-central Germany; Germanys principal industrial region.
The New Dictionary of Cultural Literacy, Third Edition. 2002., http://www.bartleby.com/59/15/ruhrvalley.html
A region of northwest Germany along and north of the Ruhr River, which flows about 233 km (145 mi) westward to the Rhine River near Duisburg. The industrial development of the region began in the 19th century.
The American Heritage® Dictionary of the English Language: Fourth Edition. 2000., http://www.bartleby.com/61/17/R0341700.html