Bug (bōg, bŭg) [key], Pol. Bug, Ukr. Buh or Zakhidnyy Buh, river, c.480 mi (770 km) long, rising in the Volhynian-Podolian hills, W Ukraine. It flows N along the Polish-Ukrainian and Polish-Belarusian borders past Brest and then NW through Poland to join the Vistula River (with the Narew) near Warsaw. It is linked with the Dnieper by the Dnieper-Bug Canal via the Pina River and with the Niemen by the Augustov Canal via the Narva River. The Bug is also known as the Western Bug.