People living along the banks of the Mekong River in Laos and Thailand were recently amazed to see the river’s water turn light blue and become so transparent that they could see the sandbars underneath. It was an eye-catching sight and the phenomenon boosted tourism to the area.

Yet the water turning blue is bad news. It shows the river is undergoing an ecological catastrophe.

The Mekong is usually reddish-brown in color as a result of nutrient-rich silt and sediments that permeate the river’s water. Silt-absorbing nutrients like phosphorus and nitrogen are carried by the water flow from upstream to downstream all the way to the open sea in the Mekong Delta in Vietnam.

Along the way the waterborne nutrients nourish aquatic species in the river as well as in its floodplains. This natural sediment system helps support an abundance of agriculture and fisheries in the region where tens of millions of people rely for their daily livelihood on the Mekong across several countries: China, Myanmar, Laos, Thailand, Cambodia and Vietnam.

Recently, however, the water has turned blue, which experts say is the result of a lack of sediments in the river, leading to a phenomenon known as “hungry river effect.”

“The current has less sediment, which unleashes energy onto the river banks downstream. This so-called ‘hungry water’ will cause much more erosion to the banks, uprooting trees and damaging engineering structures in the river,” says Chainarong Setthachau, an expert at the Faculty of Humanities and Social Science at Mahasarakham University in Thailand.

“The Mekong River with the lack of sediments will affect ecological systems in the river tremendously because the reduction of nutrients carried by the water will impact algae and both small and big aquatic vegetations,” Chainarong continued. When there is a scarcity of aquatic vegetation, aquatic animals like herbivorous fish will decrease in number and so then will carnivorous fish that prey on them, he explained.

Experts are laying the blame on the myriad of dams being built upstream in China and Laos. Thanks to robust investment from China, Laos, a landlocked mountainous nation, seeks to become “the battery of Asia” by help of new hydroelectric dams constructed on local rivers, including tributaries of the Mekong. At the moment 46 hydropower plants operate in Laos, providing a capacity of 6,400 MW. Another 54 are under construction and scheduled to go online in coming years.

The country’s government sees dams as a steady source of revenue for the communist holdout, which is one of the poorest nations in Asia. Yet the ecological costs of such development are bound to be critical, experts have warned. A study done by the Mekong River Commission reports that sediments in the Mekong are expected to be reduced by 67% and by 97% in 2020 and 2040, respectively.

These drastic drops are caused by the accumulation of sediments in water stored in reservoirs for hydroelectric dams around the Mekong basin. “The loss of sediment is expected to have damaging consequences on the productivity of the river, geomorphology and persistence of the Delta landform itself,” the report states.

“If these so-called development projects continue, especially the construction of more dams, the Mekong will face a crisis,” stresses Niwat Roi-kaeo, president of the Rak Chiang Khong Group, an environmentalist group based in Thailand’s northernmost region by the Mekong.

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