river in west-central Poland, flowing 502 miles (808 km) north and west from its source near Zawiercie in the Silesian-Kraków uplands to its confluence with the Oder River at Kostrzyn in the western part of Lubuskie province.

The Warta is the second longest river lying entirely in Poland; its basin of 21,084 square miles (54,607 square km) makes it the third largest in Poland. About half its length, from Kostrzyn to Konin, is navigable. The Warta drops 1,224 feet (373 m) from its headwaters to its mouth. The river drains a largely agricultural area of the Polish plain. Częstochowa, Konin, Poznań, and Gorzów Wielkopolski are major cities along its course.