The Warta is a river in western-central Poland, a tributary of the Oder River (Polish: Odra). With a length of approximately 808 kilometres (502 mi) it is the country's third-longest river. The Warta has a basin area of 54,529 square kilometers (21,054 sq mi) and it is navigable from Kostrzyn nad Odrą to Konin, approximately half of its length. It is connected to the Vistula by the Noteć River and the Bydgoszcz Canal (Kanał Bydgoski) near Bydgoszcz.

It rises in the Kraków-Częstochowa Upland at Kromołów in Zawiercie, Silesian Voivodeship, flows through Łódź Land, Greater Poland and Lubusz Land, where it empties into the Oder near Kostrzyn at the border with Germany.

The Greater Polish Warta Basin was the original Poland; it is said that the Polans (Polish: Polanie), a West Slavic tribe, settled the Warta Basin in the 8th century. The river is also mentioned in the second stanza of the Polish national anthem, "Poland Is Not Yet Lost."

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