Cambodia: Reversal of the River             Cambodia's Tonlé Sap is a marvelous topographic feature of the land that encompasses both a lake (‘the Great Lake') and a river system. The largest freshwater lake in Southeast Asia during the monsoon season, it is also a designated UNESCO biosphere reserve. The Tonlé Sap connects to the Mekong River (one of the world's major rivers running at 4,350 kilometres long) and responds to the Mekong's swelling and contraction of water levels. The wonder of the ‘Reversal of the River' phenomena has been celebrated by Cambodians for well over 200 years. During the months of July to October, the Mekong waters rise with the monsoon rains, ‘backing up' into the Tonlé Sap river and flooding the Tonlé Sap Great Lake - resulting in its expansion of some six times from its usual surface area - from 2,700 kilometers to 16,000 kilometers. The Bonn Om Touk water festival in November signals the subsiding of the waters, in which the Mekong ‘shrinks', triggering the famous ‘Reversal of the River Flow' - when the Tonlé Sap river reverses its current and its waters drain back into the Mekong, leaving behind a rich layer of silt. Both the flooding and the draining are regarded as essential for fertilizing the surrounding areas.