​WUPPER, a river of Germany, a right-bank tributary of the Rhine, rising in the Sauerland near Meinerzhagen. The most remarkable part of its course is that in the so-called Wuppertal. In this section, 30 m. in length, it passes through the populous towns of Barmen and Elberfeld and supplies water-power to about five hundred mills and factories. Leaving the hills above Opladen, it debouches on to the plain and enters the Rhine at Rheindorf between Cologne and Düsseldorf, after a course of 63 m.