The Bassac River (Khmer: ទន្លេបាសាក់; Tonlé Bassac) or Hậu River (Vietnamese: Sông Hậu 瀧後 or Hậu Giang 後江) 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. The name Bassac comes from the Khmer prefix pa ("father" or "male") added to sak (សក្តិ) ("power, honor"), a Khmer word borrowed from the Sanskrit sakti (शक्ति).
The Bassac River is an important transportation corridor between Cambodia and Vietnam, with barges and other craft plying the waters. A city of the same name was once the west-bank capital of the Kingdom of Champasak. Sak (សក្តិ) can also be seen in the Khmer spelling of Champasak: ចំប៉ាសក្តិ. 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 Vietnam War.