Tonle Sap (Great Lake), Siem Reap, Cambodia.
Tonle sap is the largest freshwater lake in South East Asia and is an ecological hot spot that was designated as a UNESCO biosphere in 1997. For most of the year the lake is fairly small, around one meter deep and with an area of 2,700 square km. During the monsoon season, however, water flows up from the Mekong river into the lake, increasing its area to 16,000 square km and its depth to up to nine meters. The floodplain provides a perfect breeding ground for fish.