Duong Cong To checks the water of the Hau River next to his house and he is not happy at all.
“It’s too clean,” he says.
The 72-year-old has spent all his life by the river, one of two tributaries of the Mekong and the main source of alluvium for fish farms and plantations in southern Vietnam.
Over the past years he has noticed a significant change in the river: it keeps changing its color from a reddish brown to an ocean-like blue.
“The water should look red. Now it's crystal clear like there’s nothing in there.”
Farmers and fisherfolk like To depend on the river for their livelihoods. They may not understand deeply about the science behind all of this, but they know all too well that clean water means a serious lack of alluvial sediments for fishery and agriculture.
"This used to be a great home for fish and shrimp," he recalls.
To says just five years ago, when the river was still red, nearly 200 families in his village made a living by fishing and they earned well most days.
Now only around ten people stay with fishing, and they can only catch fish during high tides, he says.
The World Wide Fund for Nature reported that suspended sediment load in the Mekong Delta declined from 160 million tons in 1992 to 75 million tons in 2014 due to the construction of hydropower dams and reservoirs on the mainstream and branches of Mekong River.
It noted that sand mining activities were also making the situation worse in many Mekong Delta provinces .
Farmers say there have been fewer fish in the river and some kinds have disappeared. Photo: Dinh Tuyen
“Hydropower dams upstream are causing this problem,” Duong Van Ni, a lecturer of environment and natural resources at Can Tho University, said.
Ni said the farmers’ observation reflects “a tragic situation.”
“The Mekong Delta is losing an irreplaceable source of alluvium.”
“My studies show that no sand or gravel has flowed downstream the past seven years,” he said.
Nguyen Huu Thien, an independent researcher of the Mekong ecology, confirmed the findings.
“Sand and gravel have been completely blocked by the dams,” Thien said.
China has received a lot of international criticism for building seven hydropower dams on the upper Mekong, with 21 more in planning. Two others are under construction in Laos.
Ni said that when China discharged water from its dams in March and April to ease the severe drought in the region, many people were easily fooled that hydropower dams are only related to one problem, which is water shortage.
But a more serious matter is the loss of sedimentation.
“When it is lost, it will never be recovered and the lack of it will lead to scary scenarios including erosion and sinking,” he said.
Studies showed that the delta has been sinking one to two centimeters every year between 2000 and 2010.
Thien even painted a dark picture in which the Mekong Delta, home to 20 million people, will be entirely gone.
“It will happen sooner or later. It will happen faster than anyone can imagine,” Thien said.