Tonle Sap
From dKosopedia
Tonlé Sap (meaning Large Fresh Water River but more commonly translated as Great Lake) is a combined lake and river system in central Cambodia. The only major river in the world to annually reverse its course, the Tonle Sap river feeds the largest freshwater lake in South East Asia. The Tonle Sap and the Mekong meet at Phnom Penh, the capital of Cambodia.
For most of the year the lake is a surprisingly shallow but large body of water, approximately one meter deep and with an area of 2,700 square km. During the monsoon season the Tonle Sap river which connects the lake with the Mekong river reverses its flow. Water from the Mekong River flows up the Tonle Sap river into Tonle Sap lake, increasing its area from 2,700 to 16,000 square km and its depth to from 3 to to 9 meters. The ancient Khmer capital of Angkor is on the northeastern shore of the Tonle Sap lake outside the modern city of Siem Reap.