The delta has an extensive system of canals and green paddy fields that stretches for kilometres, creating a part of the world that seems blessed with abundance like a virtual Garden of Eden. Local people are down-to-earth, but troubled by the increasingly frequent and serious saltwater intrusion, which destroys their crops, while the riverbanks and seashore are eroding at an alarming rate.

One farmer in Kien Giang province, who asked to be known just as “Tron”, told reporters on a recent field trip that her farm was threatened by saltwater intrusion and erosion every year – and the problems seemed to be getting worse.

“Last year I had to replant almost all of the starfruit trees in my orchard, because the saltwater encroached deep into the river in the dry season and killed most of my fruit trees,” Tron said, pointing to a line of small trees behind a bamboo fence.

“The saltwater also affected my paddy field and significantly reduced the rice yield.”

Damage from saltwater intrusion has slashed her family’s income from around US$5,000 (Bt170,000) annually in a normal year to just $1,000, which was not enough to feed the whole family, as she was responsible for her elderly mother and four children.

River basin management expert and lecturer at Can Tho University Nguyen Nhan Quang said food security and the well-being of people in the delta were at stake, as upstream projects were causing devastating impacts on Vietnam’s rice basket and the damage was intensifying.

Nguyen said the dams upriver were blocking the flow of sediment to the delta and contributing to shoreline erosion along the coast, while water-diversion projects would cut the amount of freshwater and increase saltwater intrusion.

“Vietnam has already experienced serious impacts from the development projects upriver and the situation tends to get worse to the point where it is damaging the main food source and people’s livelihoods can’t be ensured, as more projects such as the Pak Beng Dam and the Khong-Loei-Chi-Mun water-diversion project are progressing,” he said.

“Vietnam is the farthest downstream country, so we will see the most impact from developments upriver, as water quantity, water quality and sediment flow will change drastically and harm the economy of the region, which is based on agriculture and fisheries.”

The Mekong Delta has a population of at least 17.4 million people, nearly 20 per cent of Vietnam’s population, according to a census in 2013. But the fertile region produces 53 per cent of the country’s rice, 78 per cent of its fruit and 80 per cent of its freshwater fish, said Le Anh Tuan, head of the Delta Research and Global Observation Network Institute.

“The delta is facing double trouble from the impact of development projects upstream and threats from climate change. These seriously jeopardise food security, violate people’s rights and cause social disorder,” Le said.

“How can humanity achieve its sustainable development goals if we allow such harm to jeopardise the social security of the people?”

In Thailand, deputy head of the Royal Irrigation Department (RID) Somkiat Prachamwong said he could understand how people in Vietnam would be worried about projects upstream. But he added that the Khong-Loei-Chi-Mun water diversion project would not have a significant impact on the lower Mekong, as there would be a proper Environmental Impact Assessment (EIA) on the project.

“We already finished a feasibility study for the project in April and right now we are going to conduct an EIA. Then after the EIA is approved, we shall submit the project to the Mekong River Commission to start the Prior Notification, Prior Consultation and Agreement process,” Somkiat said.

He added that the project would not cause a water shortage downstream, as it would mostly operate in the rainy season. Moreover, the water levels of the Mekong were already regulated by Chinese dams and there was more water flowing in the dry season.

The Khong-Loei-Chi-Mun project aims to increase the irrigated area in Thailand’s Northeast by up to 1.58 million rai (250,000 hectares) by diverting water from the Mekong through the Loei River and then via irrigation canals across the region.

Meanwhile in Laos, many hydro projects are progressing rapidly. The Xayaburi Dam, the first dam on the lower Mekong, is 70 per cent complete and due to start operating in 2019. A second dam, the Don Sahong, is also under construction and already 25 per cent finished. A third dam at Pak Beng is due to finish the consultation process next week. The Lao government and proponents of the dams say they were designed with an environmentally friendly sediment flush system to help boost the flow of sediment downstream.

Nevertheless, Nguyen said states in the river basin were still focusing on benefits for their own countries and ignoring negative impacts that their neighbours downstream would endure.

“We have to be sincere in working with our neighbours in order to assure sustainable development for us all, otherwise we will kill the Mekong River and endanger millions of people along its banks,” he said.