Bug is a name of two rivers in eastern Europe on opposite sides of the European watershed. The (western) Bug flows through western Ukraine, south-western Belarus and Poland. It is 772 km long and empties into the Vistula. The basin of Bug is about 30,420 km2 large.
The Western Bug is the boundary between Poland and Ukraine. It ends in the Narew River near Serock and it is 772 km (480 mi) long, making it the fourth longest river in Poland.
The Southern Bug is another river in Ukraine. Its source is in the west of the country and it flows into the Black Sea. It is 806 km (501 mi) long.