In late October or November, something amazing happens to the Tonle Sap River. Its flow actually changes direction! For the entire monsoon season, the Tonle Sap River pushes water from the Mekong into the Great Lake. This increases the lake's size tremendously. For most of the year, the lake is only about a meter deep with an area of 2,700 square kilometers. The Tonle Sap pushes enough eater into the lake to make it nine meters deep with an area of nesrly 16,000 square kilometes!