Threat from sand mining places Southeast Asia's largest freshwater lake at severe risk

by Sophie Jenkins
London, UK (SPX) Nov 11, 2025

Intense sand mining is destabilizing Tonle Sap Lake, Southeast Asia's largest freshwater lake and a UNESCO Biosphere Reserve. New research has pinpointed sand extraction in the Mekong River as the principal driver behind the decline of the lake's vital reverse flow, a system that controls water levels and supports fish populations for millions of people.

The study reveals that more than 100 million tonnes of sand are removed each year from the Mekong's riverbed, with most of this extraction driven by the construction industry. The practice has led to substantial riverbed incision, intensifying year-on-year and weakening the flood pulse that fills Tonle Sap during the monsoon season.

Tonle Sap's reverse flow system depends on monsoon-driven rising waters in the Mekong, which temporarily reverse the Tonle Sap River and refill the lake. This process turns the lake into a flood regulator for the Mekong Delta, supporting 23 million people downstream and providing feeding habitats for 885 species, including endangered animals.

Between 1998 and 2018, riverbed lowering attributable to sand mining and sediment trapping by dams has diminished reverse flows by up to 50 per cent. The study projects that, unless current rates of sand extraction are reduced, the flood pulse may fall by nearly 70 per cent by 2038 compared to 1998 levels.

"Climate change and upstream dams play minor roles, but riverbed incision from sand mining is by far the dominant factor," said Steve Darby, Professor of Physical Geography at the University of Southampton.

Riverbed levels across Cambodia and Vietnam have dropped by up to three metres in two decades. According to Professor Darby, "at this rate, the lake system faces near collapse within 10 years, threatening ecosystems, livelihoods, food security and heightening flood risks throughout the region."

The international research team is continuing to map the environmental and economic dangers associated with aggressive sand mining. The Southampton-led Hidden Sands project is measuring impacts on communities and collaborating with Vietnamese agencies on risk-based sand mining governance.

Craig Hutton, Professor of Sustainability Science and director of Southampton's Sustainability and Resilience Institute, stated, "the lake feeds some six million people, providing 60 percent of Cambodia's protein, but disruption from sand extraction, deforestation, illegal fishing and chemical use is damaging fish production."

During recent fieldwork, Professors Hutton and Kemp recorded widespread mortality in aquaculture, declining wild fish catches and increasing household debt. "One fisher told us, 'We just want another life for our children now. Anything but fishing,'" reported Professor Hutton.

Research Report:Sand mining driven reduction in Tonle Sap Lake's critical flood pulse