Main (mĪn) [key], river, c.310 mi (500 km) long, formed near Kulmbach, E central Germany, by the confluence of the Roter Main and the Weisser Main, both of which rise in the Fichtelgebirge. It then winds generally west through the rich farmland of central Germany and past the industrial areas of Schweinfurt, Würzburg, Aschaffenburg, and Frankfurt to the Rhine River at Mainz. Navigable from its junction with the Regnitz River, its chief tributary, the Main is an important east-west route. The Ludwig Canal connects it with the Danube River. A recently completed addition to the canal links the Danube with the Rhine, allowing barge traffic from the North Sea to the Black Sea, a distance of more than 2,000 mi (3,200 km). There are about 40 hydroelectric power plants on the Main, of which Griesheim (62,000-kW capacity) is the largest.