The Bug River (Polish: Bug [buk] ( listen); Ukrainian: Західний Буг, Zakhidnyy Buh or Western Bug; Belarusian: Захо́дні Буг, Zakhodni Buh; Russian: Западный Буг, Zapadnyy Bug) is a left tributary of the Narew river flows from central Ukraine to the west, passing along the Ukraine-Polish and Polish-Belarusian border and into Poland, where it empties into the Narew river near Serock. The part between the lake and the Vistula River is sometimes referred to as Bugo-Narew. The Vistula River drains into the Baltic Sea.

The Bug is 830 km long (587 km in Poland)^{[citation needed]} and is the 4th longest Polish river. The basin area is 39,420 km² (19,284 km² in Poland). It is connected with the Dnieper river by the Dnieper-Bug Canal.

Traditionally the Bug was also often considered the ethnographical border between Orthodox and Catholic peoples. The Bug was the dividing line between German and Russian forces following the invasion of Poland in the Second World War.

Poltva, Sołokija, Bukowa, Huczwa, Uherka, Włodawka, Krzna, Liwiec, Ług, Mukhavets, Leśna, Nurzec, Brok, Warenzhanka

Bug may refer to:

A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including stream, creek, brook, rivulet, tributary and rill. There are no official definitions for generic terms, such as river, as applied to geographic features, although in some countries or communities a stream may be defined by its size. Many names for small rivers are specific to geographic location; one example is "burn" in Scotland and northeast England. Sometimes a river is said to be larger than a creek, but this is not always the case, because of vagueness in the language.

Rivers are part of the hydrological cycle. Water within a river is generally collected from precipitation through a drainage basin from surface runoff and other sources such as groundwater recharge, springs, and the release of stored water in natural ice and snowpacks (e.g., from glaciers). Potamology is the scientific study of rivers.