Opava

The Opava (Polish: Opawa, German: Oppa) is a river in the Czech Republic, a left tributary of the Oder River. It partly forms the Czech-Polish state border. It flows through the Moravian-Silesian Region in the Czech Republic and along the Opole Voivodeship in Poland. It is formed by the confluence of the Černá Opava and Střední Opava streams. Together with the Černá Opava, which is its main source, the Opava is 129.3 km (80.3 mi) long, making it the 15th longest river in the country. Without the Černá Opava, it is 110.7 km (68.8 mi) long.

Source: Wikipedia https://en.wikipedia.org/wiki/Opava_(river)