Oder (ōˈdər) [key], Czech and Pol. Odra, river, 562 mi (904 km) long; the second longest river of Poland. It rises in the E Sudetes, NE Czech Republic, and flows generally NW through SW Poland, then N along the Poland–Germany border to the Baltic Sea N of Szczecin, Poland. The Warta and the Lausitzer Neisse rivers are its chief tributaries. There are power dams on the Oder's headwaters in the Czech Republic. Navigable from Racibórz, Poland, the Oder is an important waterway of central and eastern Europe, connecting the industrial region of Silesia with the sea. Barges on the river carry iron, coal, and coke. The Oder is linked by canals with the Spree and Elbe rivers; the Warta connects it with the Vistula River. Wrocław, Frankfurt an der Oder, and Szczecin are the chief cities on the Oder.