Mekong basin's vanishing fish signal tough times ahead in Cambodia

“Snake, catfish, elephant fish …” he says, his eyes crinkled against the sun. “Before, a long time ago … the lake had a lot of catfish.”

But in just one generation, everything has changed. Fish species are dwindling, plant life is dying and the entire Mekong system is breaking apart. For the children gathered around Tbong, a plentiful Tonlé Sap is nothing but a story.

Situated in the heart of the lower Mekong basin, Tonlé Sap is the largest freshwater lake in south-east Asia. The lake and its surrounding floodplains were designated a Unesco biosphere reserve in 1997 and the lake supports the breeding, feeding and harvesting of hundreds of species of fish and other freshwater produce.

But this year the waters have fallen to a record low.

“Not only have the water levels across the lower Mekong River never been so low since the creation of the Mekong River Commission (MRC) in 1995, but the water is also unusually blue [due to the loss of suspended sediments],” says Marc Goichot, senior adviser for the WWF’s greater Mekong programme.

“Blue may be good for the Caribbean Sea, but for the Mekong it is not natural and bad news, [it’s] a big change in the ecosystem that will have a wide range of impacts including exposing vulnerable aquatic species to predators, weakening riverbanks [and] starving rice fields, mangroves and fish of the rich nutrients they need.”

While the climate crisis has exacerbated the problem – prompting even Jeremy Clarkson, host of the Grand Tour, to acknowledge the effects of the climate crisis for the first time – scientists have been warning of changes in the Mekong basin for decades.

The idea of damming the lower Mekong dates back to the cold war when the US, Soviet Union and China began to look at hydropower as a potential strategy for economic development. It gained momentum in the early 2000s. At the time, the MRC estimated that its four member states – Cambodia, Vietnam, Laos and Thailand – could expect benefits of $30bn (£23bn).

But years later, the commission revised its projections, stating that the environmental losses associated with these dams outweighed any potential profit.

Despite these warnings, China now operates eight megadams and lower Mekong states are persisting with plans for their own hydropower plants. In Laos and Cambodia alone, more than 140 dams are planned on the main river and its tributaries.

In dividing the Mekong River into reservoirs, hydropower dams block the flow of nutrient-rich sediment downstream, changing the shape and depth of the riverbed and riverbanks. Between 1992 and 2014, suspended sediment load in the Mekong basin was more than halved, according to the WWF.

As the sediment has become blocked, seawater has begun to intrude farther up the river, threatening its delicate freshwater ecosystem. The river eats into its own riverbanks and riverbed to replace the sediment, exacerbating the problem, and sand dredgers dig out whatever is left.

The dams also block the movements of about 160 species of fish in the Mekong basin that rely on long distance migration.

“[They] need to travel far upstream (northern Laos) to spawn, and the juveniles need to travel back to the large floodplains of the Mekong delta and Tonlé Sap lake to feed,” says Goichot. “Any obstacle to this migration would have a very high chance of leading to their extinction.”

Larger species have a longer migration route and so have been hit the hardest. In 2010, populations of the Mekong giant catfish had dropped 90% in the last decade.

“The Siamese flat-barbelled catfish, which was present in the region, was declared extinct in 2013. Of the 692 extant freshwater fish species known to occur in the lower Mekong basin, 68 (10%) are globally threatened with extinction and a further 22 (3%) are near threatened,” the MRC noted in its State of the Basin report in 2018.

The decline is not just due to environmental changes. The black market for Tonlé Sap’s freshwater fish is a thriving international business.

It’s obvious that it’s a sensitive topic when you get down to the lake. No one is particularly keen to talk. Boat owners aren’t sure what they do for a living, market sellers have forgotten the price of their fish, and some don’t even remember where they got them. This may be because they can’t be sure whether their fish was caught legally or not.

Many perpetrators are local people, driven by desperation. The UN’s Food and Agriculture Organization reports a range of illegal methods, including explosives, electro-fishing, poisoning, and giant and unauthorised nets.

It is also common for people to ignore fishing bans during the closed season from June to October, when certain areas are off limits to allow fish to spawn.

A lot of the larger illegal fish caught in Tonlé Sap go to Vietnam, where the larger fish in particular are believed to bring good luck and boost sexual performance. Trading these fish is outlawed under both international law and domestic Cambodian and Vietnamese rules, but enforcement is weak. Vietnamese traders buy them from Tonle Sap fishermen at exorbitant prices for specialty restaurants back home.

The impact of this black market trade, alongside the damming, sand dredging and other human activities, is becoming increasingly clear.

As one of the world’s largest producers of inland fish, Cambodia relies on the Mekong to a large extent for its food security. Across the lower Mekong basin the share of protein in the average diet that comes from freshwater fish is between 2.2 and 8.6 times the world average.

For those who live close to Tonlé Sap, fish has traditionally been free but people are now having to buy it, and at ever rising prices. According to one Siem Reap market seller, Vannak, the cost of fish is more than double what it was a few years ago. “Five or 10 years ago [we bought] one kilo for 4,000 or 5,000 riel ($1.20),” he says, pointing to the fish he is grilling. Now the fish – “trey rors”, a local staple – costs 10,000 riel a kilo.

Tbong remembers a time when you could simply put up your net in the mangroves and the fish would catch themselves. “Now, when I go fishing it’s not only one day, two days [then I] come back. For around 10 or 15 days I stay in the centre of the lake,” he says.

As wild fish become increasingly rare, fishermen are creating aquaculture farms cut into pieces of the lake, while Cambodia is turning to alternative protein sources. But these are likely to have significant ecological impacts.

“Other sources, that could be beef, soya or aquaculture, they all use land and water [and] they pollute,” says Goichot. “This means other options for producing protein will put more pressure on land, and will probably push to more forest conversion [and] more competition between sector and domestic use of water.”

What is happening in Tonlé Sap is a very real indication of what is to come for the entire Mekong basin if exploitation of its resources continues unchecked, experts say. But as yet responses have been slow.

“The MRC has been relatively successful at generating knowledge,” says Goichot, “but has not had much success in finding common ground or consensus on important decisions, notably hydropower or the management of sediments.”

Some strategies are in place. Vietnam’s prime minister signed resolution 120 in 2017, outlining a vision for sustainable development in the Mekong delta up to 2100. And environmental organisations continue to push for closer collaboration between the government and business sectors.

Under its Resilient Asian Deltas initiative, WWF is working to secure political and financial investment for “building with nature” when planning development. Under a separate initiative the organisation is also seeking to implement a strategy for water stewardship.

“This aims to get industry to take collective action and contribute to tackling river challenges beyond their fence line,” says Goichot, “and in the end to have a positive influence on the governance of river systems.”

This kind of governance is not only essential to the future of the Mekong, it is urgent. According to an MRC study conducted from 2012 to 2017, there will be a 35–40% reduction in biomass by next year if no action is taken.

“Hydropower development through 2040 will eliminate migratory fish in large parts of the Mekong. No Mekong migratory fish species will be able to survive in the reservoirs of dams planned by 2020 and 2040,” the report warns in its summary.

Goichot concludes: “The Mekong ecosystem is clearly experiencing major changes that are very concerning; how far are we from a major crisis?”