Tonle San

Tonlé San
Map of Cambodia with Tonlé San river marked
Native name	Sông Sê San
Other name(s)	Ya Krong Po Ko
Country	Vietnam, Cambodia
Basin features
Main source	confluence of Dak Psi and Dak Po Ko 14°36′23″N 107°50′25″E / 14.6063°N 107.8404°E / 14.6063; 107.8404
River mouth	Mekong 13°32′10″N 105°57′54″E / 13.536°N 105.965°E / 13.536; 105.965Coordinates: 13°32′10″N 105°57′54″E / 13.536°N 105.965°E / 13.536; 105.965
Progression	Tonlé San—Mekong—Mekong Delta—South China Sea
Basin size	17,000 km2 (6,600 sq mi)

Tonlé San, also known as Tonlé Se San or Sesan River, is a river that flows through central Vietnam and north-east Cambodia. It is a major tributary of the Mekong River. A short portion of the river forms a part of the international border between Cambodia and Vietnam.