During the Cambodian Civil War, massacre of the Vietnamese minority results in 800 bodies flowing down the Mekong river into South Vietnam.

The Cambodian Civil War was a civil war in Cambodia fought between the Communist Party of Kampuchea against the government of the Kingdom of Cambodia and, after October 1970, the Khmer Republic, which had succeeded the kingdom after a coup. The conflict was part of the Second Indochina War (1955–1975).

Vietnamese Cambodians refers to the ethnic group of Vietnamese who live in Cambodia or Vietnamese who are of full or partial Khmer descent. According to Cambodian sources, in 2013, about 15,000 Vietnamese people live in Cambodia. A Vietnamese source stated that 156,000 people live in Cambodia, while the actual number could be somewhere between 400,000 and one million people, according to independent scholars. They mostly reside in southeastern parts of Cambodia bordering Vietnam or on houseboats in the Tonlé Sap lake and Mekong rivers. The first Vietnamese came to settle modern-day Cambodia from the early 19th century during the era of the Nguyễn lords and most of the Vietnamese came to Cambodia during the periods of French colonial administration and the People's Republic of Kampuchea administration. During the Khmer Republic and Khmer Rouge governments in the 1970s under the Pol Pot regime, the Vietnamese among others were targets of mass genocides; thousands of Vietnamese were killed and many more sought refuge in Vietnam.

The Mekong or Mekong River is a transboundary river in East Asia and Southeast Asia. It is the world's twelfth-longest river and the third-longest in Asia with an estimated length of 4,909 km (3,050 mi) and a drainage area of 795,000 km² (307,000 sq mi), discharging 475 km³ (114 cu mi) of water annually. From its headwaters in the Tibetan Plateau, the river runs through Southwest China, Myanmar, Laos, Thailand, Cambodia, and southern Vietnam. The extreme seasonal variations in flow and the presence of rapids and waterfalls in the Mekong make navigation difficult, though the river remains a major trade route between Tibet and Southeast Asia. The construction of hydroelectric dams along the Mekong in the 2000s through the 2020s has caused serious problems for the river's ecosystem, including the exacerbation of drought.