Tonlé Sap or Cambodian Lake is a system of rivers and lakes of great importance to Cambodia. This is Southeast Asia's largest freshwater lake and was recognized by UNESCO as a world biosphere reserve in 1997. Tonlé Sap means "large freshwater river" but is often translated as "Great Lake" in languages. other languages; "Bien Ho" is the Vietnamese name for the size of this lake that makes it invisible.