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river and major industrial region along its course, North Rhine-Westphalia Land (state), western Germany. The river, an important tributary of the lower Rhine, rises on the north side of Winterberg and flows 146 mi (235 km) west past Witten (the head of navigation), Essen, and Mulheim to enter the Rhine at Duisburg. The Ruhr functions chiefly as a supplier of water and is dammed in many places to form lakes and reservoirs. Nearby canals carry the bulk of the water traffic. Its chief affluents are the Mohne (right) and Lenne (left)