The Bug River (Polish: Bug [buk] or Western Bug; ; Ukrainian: Західний Буг, Zakhidnyy Buh, Belarusian: Захо́дні Буг, Zakhodni Buh; Russian: Западный Буг, Zapadnyy Bug) is a major European river which flows through three countries with a total length of 830 kilometres (520 mi).A tributary of the Narew River, the Bug forms part of the border between Ukraine and Polandfor 185 kilometres (115 mi), and between Belarus and Poland for 178 kilometres (111 mi), and is the fourth longest Polish river.