Odra is a river in central Croatia. Its source is in the Žumberak mountain, southwest of Zagreb. It flows south-east, more or less parallel to the river Sava. It flows into the river Kupa, just before the Kupa joins the river Sava near Sisak. For the Second World War frigate class, see River class frigate The Murray River in Australia A river is a large natural waterway. ... Žumberak is a mountain situated between Croatia and Slovenia. ... Zagreb (pronounced ZA-greb) is the capital city of Croatia. ... Sava also Save (German Save, Hungarian Száva) is a river in Slovenia, Croatia, Bosnia and Herzegovina and Serbia, a right side tributary of Danube at Belgrade. ... Kupa (Slovenian Kolpa) is a river in Croatia and on the border with Slovenia. ... Sisak is a city in central Croatia. ...