Danang, Vietnam - "Well I can tell you, all my fish are dead now."

Nguyen Thi Bach Vien sounds more resigned than anything else. She is calling from her home in Ben Tre province, a few hours drive south of Ho Chi Minh City in the belly of Vietnam's Mekong Delta, where she has a fish farm and gardens of coconut and pomelo trees.

Vien's freshwater shrimps and giant river prawns are dying, too.

The 62-year-old has spent her whole life on her land, watching the soil gradually change and the air grow more sweltering every year. Now she fears that she and her husband are likely to be the last of their family to work solely on the farm.

"Dead fish and dead shrimps," Vien says, "and if we don't have a solution soon, I think, dead farmers too."

The issue is water. Salty seawater has intruded into the freshwater Mekong Delta at unprecedented levels this year, to the point at which peoples' crops and produce simply cannot survive.

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The Mekong Delta is a vast spread of fertile riverbeds, islets and mangrove swamps at the end of the Mekong River, where Vietnam's coastline meets the sea. It spans about 65,000sq km (25,100sq miles) and is home to more than 20 percent of Vietnam's population.

The Mekong River feeds into it from as far north as Qinghai, China, winding down through Tibet and Southeast Asia, providing what has historically been an Eden for natural life.

There are millions of farmers like Vien across the delta suffering huge losses, but there is little they can do except hope things change before there is nothing left.

A broken system

Seawater flows into the Mekong River every year as part of the natural delta system, but it has never intruded so far or with such intensity.

Normally, the Mekong turns salty only for a month or so but, this year, farmers have had to endure at least four months of salinity and the situation seems set to continue.

Salty seawater began to enter the delta early in mid-November 2019 and by January this year, seawater was projected to reach 30-40km deeper than the annual average during the full dry season. Fast forward to mid-April, and the high salinity levels are expected to remain into May unless the monsoon season can help reset the balance.

Higher salinity levels are due to several factors, including a lack of fresh water washing downstream into the delta, and a deepening riverbed. This has been, to some extent, compounded by the effects of climate change.

A map showing water salinity levels across the Mekong Delta [Zoe Osborne/Al Jazeera]

When the Mekong system is functioning normally, it floods every wet season. Fresh water from upstream surges through the delta and into the sea.

Cambodia's Tonle Sap Lake, reportedly responsible for 30-35 percent of the delta's water supply, is filled by these floods and then, in the dry season, it slowly discharges water into the delta. This allows fresh water to continue to wash seawater out despite there being no rain.

The lake would usually be fully drained by around March, which would result in higher salinity, but only for a month or so until the monsoon came and the Mekong Basin began flooding once again.

One month is manageable for farmers who would simply save water for the salt season.

"People would always have barrels of water ready. My farm has five ponds with which we collect rainwater throughout the year," Vien says.

But this year, Tonle Sap did not fill up and the salt has sat in the delta for months on end.

The main culprits are upstream dams, which control water and sediment levels during the monsoonal floods, and sand mining, which is depleting the riverbeds.

The upstream dams

There are 11 existing dams in China, two in Laos in the Lower Mekong Basin, and at least 300 on tributary waterways. The dams use floodgates to release the wet season floods in a more controlled manner.

"[The] water eventually leaves the dams, but with a little bit of a slower pace," says Sepehr Eslami, a coastal engineer, senior researcher and adviser for Utrecht University and Deltares in the Netherlands.

This prevents Tonle Sap from filling during the monsoon because the peak discharge is no longer there. This means there is then less to run into the Mekong Delta which, according to Sepehr, is lacking 10 billion cubic metres (2.64 trillion gallons) of water during the dry season.

Rice farmers all over the delta are losing their yields to the salt and the drought [Zoe Osborne/Al Jazeera]

"The river is dead," says Tran Tho Tu, a rice farmer in Ben Tre province. "There's not even water for humans, let alone the farms and the animals. We are having to pay hands over knuckles for water [just] to cook."

Abnormal weather linked to climate change compounds the issue. In 2019, the monsoon transition (from the wet season to the dry season) came early, which also affected water levels in the Tonle Sap Lake. Then the drought started earlier and has still not ended. But this is only a minor factor.

"Had the dams not been built and [if] sand mining would be limited, this would never be a big problem," says Sepehr. "The drought event happened at the same time when a new dam [Xayaburi Dam] was filling [in October] and because of that, the effect of this small drought event was exacerbated to an out-of-control level."

A bit of rain finally fell this week, but the full monsoon is not expected until mid-May.

Sand mining and deepening riverbeds

Another key factor is the declining amount of sand, silt and gravel - sediment - being deposited on the riverbeds of the Mekong Basin. Dams upstream not only interfere with the natural flow of water but also block sediment from flowing downstream. This deepens the Mekong riverbed, allowing higher quantities of heavier seawater to wash in.

The dams take millions of metric tonnes of sediment out of the Mekong River every year.

This not only means that there is less sand to line the riverbed, it actually encourages erosion, compounding the problem. When the river does not have enough sediment, it gouges it out of the riverbed and banks.

"At the same time, you have downstream sand mining," says Sepehr, which is a form of mining whereby sand is extracted from riverbeds using excavators or strong pumps. "The magnitudes [that sand miners remove] are not only huge in Vietnam, but also huge in Cambodia. We are talking ... 50-100 million tonnes per year."

The extracted sand is used largely for urban development. The mining process drastically disturbs riverbed ecosystems. It causes river banks to erode and digs deeper into the riverbeds, which lets more saltwater in, making the delta infertile.

A diagram showing the flow of water and the loss of sediment [Zoe Osborne/Al Jazeera]

Historically, about 160 million tonnes of sediment was transported by the Mekong River every year, but this is now being drastically reduced - reduction due to the dams is up to 90 percent, while reduction due to sand mining is likely to be close to 100 percent. This not only lowers sand deposits but puts them into a serious deficit.

Mekong riverbeds are reportedly deepening by rates of 200-300mm (7.9-11.8 inches) per year.

'No spare water to wash the dishes'

The effect of these factors on local farmers is immense.

Rice farmer Tran expects to lose at least 30 percent of his rice yield this harvest because there is no fresh water to irrigate it with.

"Look at the water. It's like a mud soup now," he says. "You can't even use it to wash the pigsty, let alone use it to water your crops."

Tran, 53, farms vast fields of rice, with a small garden of herbs and fruit trees on the side that is mainly for family use. Like many Mekong farmers, he also keeps a few cows, sows, chickens and some ducks, and even has one pond of fish that feed on the waste coming in from the farm and the sty.

His family has farmed this land for 60 years, if not longer. They pull in anywhere from 10 million Vietnamese dongs ($425) to 100 million dongs ($4,254) per month depending on the time of year, the harvest they get and the prices of produce.

When Tran was young, people were born, lived and died on the river. It was a magnificent, almost frightening torrent of water back then.

"My generation, we knew how to swim before we knew how to walk," he says. "... Back then you could just eat off of the rivers ... and [there were] ricefields, as far as the eyes could see. You could get lost in them."

But now the river is dead and the rice is shrivelling. His family will have to harvest early to save what little rice is left.

Fish farmers - the Vien couple - now have to buy water for household use [Zoe Osborne/Al Jazeera]

Likewise, Vien has lost not only her fish and shrimp, but much of her pomelo garden to the salt.

"We have had to chop off all the fruit ... to save the trees," she says. "It's choosing between saving the mothers at the cost of babies, [and] losing both."

Her canals are dry and stinking. She has noticed crusts of sediment rising up the walls.

"There are sediments on the surface. Metal and natri salt and some other nasty stuff," she says. "You can smell it from metres away, and it's not a good smell."

In lieu of usable river water, Vien is having to buy fresh water for household use and, as much as possible, for the farm. Since the beginning of April, she has bought more than 10 cubic metres (2,642 gallons) for a little more than 1 million dongs ($42).

This is a lot for families like hers.

She uses Mekong water whenever she can to save as much money as possible.

"You can use it to do laundry," she says. It makes her family's clothes gritty but they endure. "The alternative is losing even more money."

Tran also buys his water. It costs him about 1 million dongs ($42) per month and that is only for just enough water to cover the essentials, like drinking and cooking.

"At that price, we can't even spare water for doing the dishes," Tran says. "We eat out of pots and pans these days. Everybody just takes a spoon and digs in."

The sources of available water ranges. Some of it is provided by the government, some donated by charities, and some sold by private organisations - who have reportedly hiked up their prices recently, some locals told Al Jazeera.

Ngo Quang Khoa is a farmer who raises seedlings [Zoe Osborne/Al Jazeera]

Where seedling farmer Ngo Quang Khoa lives, both treated household water and untreated fresh water for use in the farms is available. The government brings household water once a week but his family does not use it. They get water carried by boats down from upstream. The water itself is free but they have to pay for smaller boats to collect it.

"[The price] depends on if we pay for the big boat or small boat," he says. "A small boat would cost us around 1 million dongs and could bring around 10 cubic metres of water, bigger boats cost 3-4-5 million dongs [$128-$212] and can bring 40-50-70 cubic metres of water."

There are charities providing water for free. Even Vietnamese celebrities have been funding seawater filters.

But the scope of this charity work is limited. Many farmers are simply having to use saltwater, whether it is viable or not.

'The food chain could collapse'

Fish farmer Dung, who farms fish and grows a small number of fruit trees in Tien Giang province, can only get enough government water to justify using it for his trees, which have a higher value. For his fish, he pumps water from the Mekong.

"The fish can still survive in saltwater, but the thing is if the conditions are not right the fish will not grow as well as they could," he says.

He raises them from when they are young and then sells them to other people to raise until they are fat enough for the market. But nowadays people do not want them.

"They are afraid to buy ... from me," he says.

As well as fish, Dung farms rice and some vegetables and fruit. Even if he can no longer farm these things, he says, he will still stay on his land and try to adapt - in his area, there is nothing but farms and those who do work in other sectors are well established. If he tried to do something else there would be too many people to compete with.

But he does worry. Losses like his are putting farmers into serious financial situations.

The market price of Dung's fish has dropped. For example, he says, he used to sell them for 40,000 dongs (nearly $2) per kilogramme but now they fetch only 15,000 dongs ($0.64) for a kg.

Many people are suffering debt because of what is happening to their farms. Everyone Tran knows is in debt, be it big or small; even he owes money.

Dung, a fish farmer, is trying to adapt to the changes [Zoe Osborne/Al Jazeera]

Unable to survive on farming alone, many families are supplementing farming with other work to get by.

"[My] area has some industrial and packaging complexes so many young people became factory workers or [have] started pursuing other careers," says Vien.

But the impact of the salt does not stop with local farmers. It could drive huge shifts on a national and even international scale.

According to Sepehr, if stakeholders continue to abuse the Mekong Basin, the saline intrusion that the delta is experiencing this year could become the norm in 10 to 20 years.

In this case, the socioeconomic implications could be extreme.

"The whole ... food chain is going to collapse," says Sepehr, "The business models will have to change. It will be very difficult for small businesses to maintain status quo ... [so] they [will] have to give up agriculture and aquaculture to larger organisations."

As a result, monopolies are likely to develop, which will impose more industrialised methods of farming.

"In this transition period, there [could] be a lot of public costs. To accommodate for the people that lose their houses, their jobs, their health ... their families," says Sepehr.

Food security could be thrown into question.

"Salt is bad for crops, notably rice have low tolerance to salt; thus early, late or salt front reaching far into land can seriously affect rice yields," says Marc Goichot, a senior adviser for the World Wide Fund for Nature's Greater Mekong programme.

"There are scenarios where [the Mekong Delta] is not going to be livable," says Sepehr. "So there will be mass migrations to other parts of Vietnam or upstream Cambodia for instance."

Too late to go back

At this point, it may not be possible to reverse the impact of human activity on the Mekong Basin.

"It took ... 20 [to 30] years ... from the start of building the dams and this increase in sand mining to create the problems we have today," says Sepehr. "If you reverse everything today, it might still take 30 years."

Pomelo Trees from Vien's garden; some farmers now have to cut off the fruit to save the trees [Zoe Osborne/Al Jazeera]

But while full recovery is unrealistic, there are still things that can be done to limit further impacts.

"Countries across the Mekong should agree on basin-wide management schemes ... controlling sand mining and stopping dam construction," says Sepehr. "The consequences of the dams are not only for the hosting country, but also downstream countries."

Some progress has been made. In March, Cambodia announced it would postpone building new hydropower dams on the mainstream Mekong for 10 years. In February, Thailand scrapped China-led plans to dredge a key section of the Mekong River.

On a local level, Vietnam established the Resolution 120, an agreement on the "Sustainable and Climate-Resilient Development of the Mekong Delta" in 2017, and has developed a national agricultural restructuring plan by the Ministry of Agriculture and Rural Development (MARD).

But overall efforts towards sustainable development have been minimal. As Marc Goichot told The Guardian, the MRC has "not had much success in finding common ground or consensus on important decisions".

"There are rumours that the Mekong water management will be in ASEAN summit agenda, but again I've seen scattered reports and not sure if it really happens," says Sepehr.

As one of the most affected countries in the Mekong Basin, Vietnam could take a more proactive role in Mekong development.

Last year Petrovietnam, a state-owned Vietnamese oil company, invested in Laos's controversial Luang Prabang dam. The move was reportedly made for geopolitical reasons - to influence dam operations rather than leaving control over the dam to China.

But influence may not be enough.

More sustainable development

"I think Vietnam has to put its diplomatic efforts into stopping the [development of the] dams, rather than investing in them to have a seat at the table," says Sepehr. "... Vietnam should have a much more active diplomacy towards pushing Laos and Cambodia."

Citizens of the Mekong Delta could have a voice in Vietnam's political movements, by pressuring the government towards more sustainable development, Sepehr adds. "I think that's a very important part of the private level."

People can also be involved in mitigation on a local level. Vietnam is already taking steps to adapt to the extreme salinity levels.

This season, a significant factor in mitigation has been early preparation. As early as last September, MARD asked delta authorities to adapt in anticipation of a serious period of salinity. These measures include planting the winter-spring rice crop a month early and instructing farmers not to grow their rice in areas that were likely to be affected by the saline intrusion.

The authorities also decided to reduce the winter-spring rice area by 100,000 hectares (247,105 acres) to save water. "There is something like 1000-2000 cubic-metres per second of water demand (usage) in the Mekong Delta for the sake of agriculture in the dry season," says Sepehr. "... When you save in agriculture, you save a lot."

Fruit farmers have built embankments for irrigation water and local authorities built more water pipes in the delta.

Locals collect water that has been brought to their area from other parts of the delta or nearby, where salt has not reached the waterways [Zoe Osborne/Al Jazeera]

Irrigation can also be improved, says Sepehr, citing the Netherlands' greenhouse technology where the system does not use huge canals, but borrows water from different sources and is more targeted. "Right now [in the Mekong Delta] they flood fields with water and ... a lot of it evaporates," he says.

Farmers have also started shifting to new forms of cultivation. In Can Tho city, rice farmers are now planting fruits, vegetables or flowers. Other rice farmers are converting to new methods of rice farming.

The WWF is working on a new model of integrated rice and aquaculture whereby both are cultivated on the same land. Under this model dykes could be opened, says Goichot, allowing flooding which would bring a range of benefits, such as natural nutrients, pest control and the replenishment of groundwater. This would reduce the need for water, fertilisers and pesticides. In the end, the volume of rice and aquaculture produced would be reduced, but their value would be higher as they could be classed as organic.

But no matter how much is done to adapt to saline intrusion, it has to be addressed at its root causes or it will only continue to worsen.

The issue has been in the spotlight for decades, and scientists have warned about it for even longer. If the Mekong Basin does not shift entirely to sustainable development, the future looks bleak.