As the Tonle Sap floodplain empties into the Mekong this spring, the Cambodians who rely on these waters face bleak prospects, with fish catches reportedly 10 to 20% of previous years. Blame for the precipitous decline in the ecology has been put on the many hydropower projects upstream.
The Tonle Sap River – pronounced Ton-lay Sap – reverses flow when the Mekong floods in summer. This floods the Tonle Sap Lake, which balloons to five times its low-water size, creating the largest lake in Southeast Asia and supplying one of the most productive freshwater fisheries on Earth.
In 2019, a combination of climate change, El Niño and dams on the Mekong and its tributaries caused the Tonle Sap River to reverse in August rather than June and for only six weeks instead of the usual five to six months. The resulting shallow, warm, oxygen-starved waters devastated the fisheries.