Fish stocks in the Mekong River in Cambodia and the Vietnamese Delta could be halved if 11 planned hydropower dams go ahead, according to the preliminary results of an extensive study funded by the Vietnamese government.
Presented yesterday at a regional conference on water, food and energy in the Mekong River Basin, the study’s results are an in-depth look into what environmental groups and fisheries experts have been warning for years: that damming the Mekong extensively will have drastic impacts on one of the world’s most important aquatic ecosystems.
Although environmental impact studies and fisheries estimates have been conducted previously, experts say that the involvement of the Vietnamese government is an indication that the results may be used as leverage against a Lao government that is increasingly pressing ahead on dam projects unilaterally.
“It’s the first time in the region that a government has put such substantial money behind a major international study and tried to bring in all the other countries in the region as participants,” said Jeremy Carew-Reid, Director of the International Center for Environmental Management.
In a presentation yesterday, Ian Cowx, the director of the International Fisheries Institute and a researcher on the study, was unequivocal in his warnings about the potential impact.
“When you have 11 dams, there ain’t a lot left by the time you get to the bottom,” he said.
In total, nine of the dams are proposed or under construction in Laos, with two of these sharing the border with Thailand, along with two proposed mainstream dams in Cambodia.
Along with having enormous hydroelectric potential, the Mekong River is a remarkably productive ecosystem. The study estimates the value of the Mekong fishery at $7 billion per year, with half of the river’s total catch in the Lower Mekong Basin here and in Vietnam.
“It’s very important for food security, with high consumption in this region,” Mr. Cowx said. “You get pretty close to the highest in the world in some areas.”
The biggest concern for the river’s ecosystem, the study found, is that the dams are expected to drastically lower the nutrients within the sediment that are key to fish survival and spawning. Not including white fish, which migrate up the length of the river, the study expects a loss of more than 60,000 tons of fish a year, mostly because of a halving of nutrients.
On top of this, the study predicts a massive impact on fish migration, especially on white fish. This is in part because of the impact of the machinery itself and also because of the reservoirs that develop as a result of the dams. Some of these reservoirs, such as at the Xayaburi Dam, extend nearly 100 kilometers upstream.
“The larvae will not drift downstream, the eggs will not drift downstream,” Mr. Cowx said. “The reservoir will act as a sump and you will lose them, and there’s no way that you can overcome that.” The impact on migration would result in an estimated 180,000 tons of white fish lost in Cambodia, the report predicts.
The scope of the toll was not limited to fish stocks, the researchers found. According to Anwar Khan, a project manager at the consultancy HDR Inc. and a researcher on the study, construction of the 11 dams would result in a 3.7 percent reduction in rice productivity in Cambodia compared to 2007 levels, as well as a monumental loss of nearly more than one-fifth of the maize crop. This is because of a reduction in the natural sediment that flows downriver. Though the overall impact on flooding would likely be minimal, the dams would have significant effects on communities within 100 kilometers downstream.
“You’re going to see a huge increase in water levels followed by huge drops in a very short period of time,” he said, referring to the Sambor Dam site in Kratie Province. “That’s when the impact on navigation is going to be felt. By the time the flow comes to Phnom Penh the impact is pretty dissipated.”
Despite Cambodia not contributing funding to the research, the Kingdom’s Mekong Committee head Te Navuth said that he will be studying the results closely. His Vietnamese counterpart, Le Duc Trung, said the two countries would form a working group to discuss the study and consult on next steps, potentially as soon as next month.
Vietnam and Cambodia have been united in opposition to the Lao government’s plan to build the Don Sahong Dam just across the Kingdom’s border. After six months of consultations through the regional Mekong River Commission, the Laotians pulled out of negotiations, saying that it was their right to move forward with the project and construction is expected to begin soon.