Odra is a river

River

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...

 in central Croatia

Croatia

Croatia , officially the Republic of Croatia , is a unitary democratic parliamentary republic in Europe at the crossroads of the Mitteleuropa, the Balkans, and the Mediterranean. Its capital and largest city is Zagreb. The country is divided into 20 counties and the city of Zagreb. Croatia covers ...

. It is 83 km (51.6 mi) long and its basin covers an area of 604 square kilometre. Its source is in the Žumberak

Žumberak

Žumberak or Gorjanci is a range of mountains or hills between Croatia and Slovenia. The highest peak is Sveta Gera on the border between Croatia and Slovenia, being tall....

 mountain, southwest of Zagreb

Zagreb

Zagreb is the capital and the largest city of the Republic of Croatia. It is in the northwest of the country, along the Sava river, at the southern slopes of the Medvednica mountain. Zagreb lies at an elevation of approximately above sea level. According to the last official census, Zagreb's city...

. It flows eastwards, passes south of Velika Gorica

Velika Gorica

Velika Gorica is the largest and most populous city in Zagreb County, Croatia. The city itself has a population of 31,341, while the municipality has a population of 63,511 inhabitants .Velika Gorica is the centre of the historical Turopolje region....

, then turns south-east, more or less parallel to the river Sava. It flows into the river Kupa

Kupa

Kupa may refer to:*Kupa River, a river in Croatia and Slovenia*Kupa River , a river in Lithuania*Kupa River in Siberia, see Kuta River*Kupa Synagogue, a synagogue in Krakow*Kupa, Hungary, a village in Northern Hungary...

 near Odra Sisačka

Odra Sisačka

Odra Sisačka is a village in Croatia. It is part of Sisak. It is connected by the D36 highway....

, just northeast of Sisak

Sisak

Sisak is a city in central Croatia. The city's population in 2011 was 33,049, with a total of 49,699 in the administrative region and it is also the administrative centre of the Sisak-Moslavina county...

, also just before the Kupa joins the river Sava.

The upper flow of Odra has been significantly altered by humans, by the digging of the 32 km (19.9 mi) long canal Sava-Odra-Sava south of Zagreb, as a measure against flooding.