Strangling the Mekong.(Mekong River in environmental danger)(Statistical Data Included)

Great civilizations have flourished along the banks of the Mekong River. The Cambodian kings who once ruled most of Southeast Asia built their glorious temples near the shores of the Tonle Sap lake, the Mekong's pumping heart. Later the kingdoms of Thailand, Laos and Vietnam variously held sway over stretches of the river until the arrival of the French in the 19th century. From its headwaters high on the Tibetan plateau, the Mekong meanders more than 4,500 kilometers through six countries. It passes through China's Yunnan province, skirts Burma, divides Thailand and Laos, splits Cambodia, spills its rich silt deposits in Vietnam and then empties into the China Sea. All told, the Mekong supports some 100 million people, who rely on the river not only for their food and water but also to irrigate crops, to travel from one place to another--and, sometimes, just to cool off on steamier days. It is, say Thais, the "mother of rivers."

Now, like so many of the world's great waterways, the Mekong is under threat. Rampant, unplanned development has begun to threaten the river's rich ecosystem, as well as the livelihood of scores of communities along its banks. Constant logging has so eroded the shoreline in places that disastrous flooding is virtually guaranteed; last year's floods in Cambodia and Vietnam killed 500 people and wiped out herds, crops and orchards. Large-scale fishing operations--some legal, some not--employ large nets and traps to catch hundreds of thousands of fish at one time. Together with poaching, this commercial fishing is wiping out certain species--among them the giant catfish and the trey riel, which gives its name to the Cambodian currency, the riel.

But the greatest danger to the Mekong may be posed by the massive hydroelectric dams--fixtures in the developing world--that have sprung up along its course. The giant cement barriers, most built in the last decade, provide electricity throughout Southeast Asia. But they also block the natural migration of fish, alter the level and quality of water and end the seasonal ebb and flow that is vital to the cycle of mating and reproduction. Pranee Nonjan, a 43-year-old Thai woman, used to fish for a living until the Pak Moon Dam was built in 1994 on a nearby tributary of the Mekong, wiping out her usual catch. She calls the structure "evil" and says, "It destroyed my family's happiness."

As in other parts of the world, dam construction along the Mekong has also led to massive deforestation, the destruction of wildlife and the displacement of tens of thousands of poor people who live along the river, chiefly ethnic minorities. That kind of damage is leading to a re-evaluation of whether the benefits of these dams outweigh their environmental and social cost. In a report last summer, the Mekong River Commission--a body that normally champions development projects in Laos, Thailand, Cambodia and Vietnam--warned that the Mekong's fragile ecosystem was "deteriorating" and added: "Should the present rate of [damage] continue, forest cover, biodiversity, fish stocks and soil quality will be harmed to levels where recovery may not be possible."

Over the last decade, the Mekong has been treated in many ways like a giant battery. Officials in China and Laos in particular have argued for the river's potential to generate power and profits--and thereby to develop the still-poor region. Beijing has already erected one massive dam, the Man Wan, across the Mekong, 100 kilometers south of the city of Dali. Two more, the Dachaoshan and the Jinghong, are scheduled to be completed and begin operations within the next two years; nearly a dozen more are in the planning stages.

The Chinese claim that the dams, meant to power the growing cities of Yunnan province, will not harm the Mekong. In fact, Beijing insists the dams will benefit downstream countries by "evening out" the river's flow, reducing it in the rainy season and boosting it in the dry season. Those opposed to the dams, on the other hand, wonder what would happen during a catastrophic drought or flood in China. Would Beijing close its sluices during droughts to preserve water, turning the downstream flow into a trickle? Would it fling open the gates during floods, releasing a wall of water that could literally wash away Thai and Laotian cities?

Those scenarios may be farfetched. But dams continue to play a key role in China's modernization drive. Some activists worry that Beijing already acts as if it owns the Mekong. "China is unlikely to change any of its developmental policies because of a negative impact beyond its border," says Chinese environmentalist Dai Qing. In fact, China has been bullying Laos for years to dynamite the river's many rocky rapids on the Laotian side to create a deep-water channel, so large cargo and passenger ships could travel from Yunnan to the sea. (China has already blown away its upriver rocks.)