Fish diversity in the Mekong River Basin is surpassed only by that of the Amazon River. A key element of the Mekong River Basin is the Tonle Sap Lake in Cambodia. The lake derives 62% of its water from the Mekong River and is the largest lake in Southeast Asia. Covering an area of 250,000-300,000 hectares during the dry season, it increases to between three and four times this size during the wet season. In 1997, the lake was nominated as a ‘Biosphere Reserve’ under UNESCO’s ‘Man and the Biosphere Program’, which aims to promote sustainable development based on local community efforts and sound science.