The Tonlé 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. The Tonlé Sap is unusual for two reasons: its flow changes direction twice a year, and the portion that forms the lake expands and shrinks dramatically with the seasons. From November to May, Cambodia's dry season, the Tonlé Sap drains into the Mekong River at Phnom Penh. However, when the year's heavy rains begin in June, the Tonlé Sap backs up to form an enormous lake.

洞里薩湖，又名金邊湖，位於柬埔寨境內西部，是東南亞最大的淡水湖。枯水期(12月—4月)湖水經洞里薩河注入湄公河，湖水平均深度為1米，面積2700平方公里；雨季因湄公河迴流，水深可達9米，面積則擴展至16,000平方公里。因為湄公河水內含沖積物質所帶來的養份，使得湖中滋生大量的魚蝦，無論旱、雨季都出產甚豐。目前洞里薩湖是柬埔寨北部的主要「肉食倉庫」，湖的周圍有逾300萬人直接或間接地以漁業為生。

http://en.wikipedia.org/wiki/Tonl%C3%A9_Sap