BANGKOK • Experts are warning that the Lower Mekong Basin may soon face depleting fish stocks, further erosion of the coastline and rising salinity that will make rice fields uncultivable.
"The facts are stronger than ever," said Mr Marc Goichot, an expert on sustainable hydropower and river basin management, who works with the World Wide Fund for Nature in Vietnam.
The mighty Mekong, dammed in the far north in China, and with 11 more dams planned or under construction, mostly in Laos, is delivering less of the nutrient-rich sediment that stabilises the coast and supports fish breeding.
Sand mining further erodes the coast, and ground water drainage to sustain human populations triggers land subsidence even as the sea level rises by around 5mm a year. Salinity is creeping inland up the Mekong delta, threatening 13,500 ha of rice fields. The result is that a 600km stretch of Vietnam's southern coast is receding at the rate of 4m to 12m a year.
As Laos goes ahead with constructing at least nine dams across the Mekong and associated rivers, the red flags are up for the future of the mighty river.
But the most alarming projection, backed by more and more scientific data, has to do with the impact of the dams on fish stocks.
An extensive, government- funded study by the Vietnam National Mekong Committee estimates the value of fish from the Lower Mekong Basin at US$7 billion (S$9.8 billion) a year. More than half of that is in Vietnam and Cambodia. The average annual per capita consumption of fish was calculated at 46kg.
But with the 11 dams, fish availability is likely to be halved in the coming years, raising uncertainty over food security, experts presenting the study's findings told the Greater Mekong Forum On Water, Food And Energy in Phnom Penh on Oct 20.
One of the study's authors and a world authority on freshwater fisheries, Dr Ian Cowx of the University of Hull's International Fisheries Institute, noted that the effect of a dam on fish migration could be mitigated, but only to some degree. Larvae and eggs do not drift downstream as they would be retained in the deep reservoirs.
More than 50 per cent of the fish species caught in the Lower Mekong Basin are migratory. These species are most at risk from dams. So-called "white fish" which migrate relatively longer distances, will suffer the most. Forty per cent of white fish in Vietnam and 37 per cent in Cambodia will be "highly vulnerable or at risk" with 11 dams, the study says.
Experts say the fact that the study is government-backed is significant as it means Vietnam is building a case with the data to persuade Laos to change its plans.
"Vietnam's approach is very sincere, they believe they are doing the right thing," a delegate at the Phnom Penh conference who asked not to be identified because of the sensitivity of the dams issue, told The Straits Times.
In recent years, discussions under the umbrella of the Mekong River Commission (MRC) have been heated. In 2011, Cambodia and Vietnam asked for a 10-year moratorium on dam-building by Laos. But beyond a mechanism called "prior consultation", the MRC is essentially toothless. Laos continued building the 1,285MW Xayabury dam, which is now about 60 per cent complete, and just weeks ago approved another controversial dam at Don Sahong.
Laos looks to energy exports to its neighbours, mainly Thailand, to boost its economy. The power and mining sector contributes to 17 per cent of Laos' GDP and nearly 70 per cent of overall exports.
"In Thailand, they are more than willing to buy cheaper hydropower from Laos to replace gas-fired power projects... so I don't notice any slowdown in power projects," Laos' vice-minister for energy Viraphonh Viravong told Reuters on the sidelines of the Singapore International Energy Week last week .