Oder

Oder, also Odra, river, north central Europe, an important transport artery. It rises near Olomouc, in the Czech Republic, and flows generally north-east into Poland, of which it is the second longest river. The Oder continues generally north past Racibórz, Opole, Wrocław, and Kostrzyń into the Baltic Sea at Szczecin. The river is 906 km (563 mi) long and navigable from Racibórz. The Oder is connected by canal with the Spree, Havel, and Elbe rivers in eastern Germany.

Before World War II the Oder flowed through German territory; with the defeat of Germany in 1945 a provisional German-Polish border was set along a line formed by the Oder and Neisse rivers. The government of West Germany delayed recognizing the new border and the subsequent loss of about 103,600 sq km (40,000 sq mi) of land until 1970. In 1990 West and East Germany united and became the Federal Republic of Germany.