Tonle Srepok is a major tributary of the Mekong River that runs between the Vietnamese province of Đắk Lắk, and the Ratanakiri and Stung Treng provinces in Cambodia. Before the development of modern roads, the river was crucially important to Lao, Khmer, and Vietnamese people for trading purposes, and as a supply line during the U.S.-Vietnam War.
Tonle Srepok (also called the Srepok or Serepok River) was along a branch of the Ho Chi Minh Trail and was used to supply North Vietnamese forces fighting in South Vietnam with weapons, ammunition, and food. When the U.S. Army discovered this, the whole area was heavily bombed, leaving behind a huge amount of unexploded ordnance that even today maims those unfortunate enough to step on or hit one. Rumors of U.S. Special Forces infiltrating Ratanakiri province abound—as to the veracity of these rumors, opinions vary.