The Tonle Sap is a combined lake and river system of huge importance to Cambodia.The area is home to many ethnic Vietnamese and numerous Cham communities living in floating villages around the lake. The Tonle Sap is the largest freshwater lake in Southeast 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, the Tonlé Sap river, which connects the lake with the Mekong river, reverses its flow. Water is pushed up from the Mekong into the lake, increasing its area to 16,000 square km and its depth to up to nine meters, flooding nearby fields and forests. The floodplain provides a perfect breeding ground for fish.