Cambodia: Sand Extraction is Causing the Disappearance of the Great Tonle Sap Lake

The global demand for sand is skyrocketing, intensifying pressure on Tonle Sap, Southeast Asia's largest freshwater lake. The extraction of this natural resource, the second most exploited after water, is significantly altering the flow of the Mekong River.

Over time, the exploitation of sand to produce concrete, glass, or fill could reduce the area of Tonle Sap, one of the most important natural habitats and fishing grounds in the region of Cambodia. In the journal Science, Brian Eyler, a water policy specialist at the Stimson Center in Washington, explains that the issue of dredging in this area has already been documented, but remains poorly understood.

In a new study, he and his colleagues highlight the consequences of these extractions on Tonle Sap, hoping that this alarming situation will finally receive the attention it deserves.

Human Activities Under Scrutiny by Reports

Stretching over 140 km, Tonle Sap has a unique hydrological characteristic in the world. Connected to the Mekong River by a river of the same name, the lake drains during the dry season and fills during the rainy season when the Mekong's current reverses. During flooding, Tonle Sap expands to six times its normal surface area and increases its volume to 80,000 cubic kilometers.

Moreover, the lake hosts around 1,400 fish species, a quarter of which are unique, as well as rare bird species. This is probably the most diverse system in the world for migratory freshwater fish, explains Alice Hughes, a conservation biologist at the University of Melbourne.

However, since the 2000s, this seasonal fluctuation has weakened. Scientists Wen Xin Ng and Edward Park demonstrated in 2021 that climate change and dams alone could not explain this decline. The real culprit appears to be sand dredging in the Mekong near Phnom Penh. By digging the riverbed, these activities prevent water from rising high enough, reducing the reverse flow that feeds Tonle Sap.

Could it shrink by 40% in less than 15 years?

The new study published by the research team confirms this link. They combined data on dredging, river depth, and water levels in a hydrological model. The results indicate a clear relationship between the lowering of the Mekong riverbed caused by sand and the changes experienced by Tonle Sap. According to their simulations, if no action is taken, flooding could decrease by 69% by 2038, the size of the lake could shrink by 40%, and dry season flows could drop by 59%. The only solution is to stop and reverse the lowering of the riverbed.

Cambodia and Vietnam have banned the export of sand, but this does not prevent dredging to meet domestic demand. Beyond Tonle Sap, the entire ecological balance and millions of people who rely on its resources are at risk.