Covering 2,600 square km (1,000 square miles) in the dry season, Cambodia's vast Tonle Sap is the biggest freshwater lake in Southeast Asia. Its unique annual cycle of flood expansion and retreat dictates Cambodia's rice production and supplies of fish. During the rainy season the Mekong River backs into the Tonle Sap River, pushing waters into the lake, which quadruples in size. In the dry season, as the Mekong lowers, the Tonle Sap River reverses its direction, draining the lake. Boats make the river journey to the lake from Phnom Penh and Battambang, tying up at Chong Khneas, 12 km (7½ miles) south of Siem Reap. Two-hour tours of the lake, costing $15 to $20, set out from Chong Khneas, and you can tour the floating villages, with prices starting at $20.
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