The "Tonlé Sap" (Khmer: "Large Fresh Water River", more commonly translated as "Great Lake") — is a lake and river ecosystem in Cambodia. Tonlé Sap is: the largest freshwater lake in Southeast Asia; a river of huge significance in Phnom Penh, Siem Reap province, and Cambodia; and an ecological hotspot that was designated as a UNESCO biosphere reserve in 1997.