Tonlé San, also known as Tonlé Se San or Sesan River (Khmer: ទន្លេសេសាន, Tônlé Sésan, Vietnamese: Sông Sê San), is a river that flows through central Vietnam and north-east Cambodia. It is a major tributary of the Mekong River. Its tributaries include the Dak Bla, Dakpsy, Sa Thầy and Lagrai rivers.^[1] A short portion of the river forms a part of the international border between Cambodia and Vietnam.

There are a number of hydropower dams on the Se San River and its tributaries. Where it joins the Srepok River in the Lower Se San 2 Dam. Upstream is the dam cascade: Se San 4A, Se San 4, Se San 3A, Se San 3, Yali Falls. On the Dak Po Ko River is the Plei Krông dam. There are also several dams on tributaries of the Dak Bla, including the Dak Snghé, tributary of the Dak Bla, is the Upper Kontum dam and hydropower plant, which discharges into the Tra Khuc River, and the Dak Doa.^{[clarification needed][2]}

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