The Bassac River (commonly called Tonle Bassac ទន្លេបាសាក់) is a distributary of the Tonlé Sap and Mekong River. The river starts in Phnom Penh, Cambodia, and flows southerly, crossing the border into Vietnam near Châu Đốc. In Vietnam it is known as the Hậu River (Sông Hậu or Hậu Giang in Vietnamese).
The Bassac River is an important transportation corridor between Cambodia and Vietnam, with barges and other crafts plying the waters. A city of the same name was once the west-bank capital of the kingdom of Champasak. USS Satyr (ARL-23), a recommissioned repair ship originally built for the United States Navy during World War II, served on the Bassac River during the Second Indochina War. Two bridges span the Bassac: the Monivong Bridge in Phnom Penh, Cambodia and the Cần Thơ Bridge in Cần Thơ in Vietnam.