Tonle Sap, a lake in central Cambodia, drained by the Tonle Sap River. During the rainy season the lake receives water from many streams, mainly the flooding Mekong River, and greatly increases in size, inundating surrounding areas. By November the floodwaters have receded. Fishing in the lake and rice cultivation along its shores are important in the Cambodian economy. North of the Tonle Sap are the ancient ruins of Angkor.