Located in Siem Reap, the Tonle Sap is the largest freshwater lake in Southeast Asia, covering 27,000 hectares in dry season (November to May) and 150,000 hectares during the rainy season (June to October). The River reverses according to the season and the Tonle Sap acts as an overflow reservoir for the huge Mekong River. It is a tranquil place to explore by boat and visitors to the area shouldn't miss the opportunity to do so. The river is vital to Cambodia's already tenuous survival as it produces 100,000 tons of fish every year - an incredible 80% of the population's protein intake.