Boat traffic at a floating market near the city of 

 Can Tho, Vietnam, jams a branch of the Mekong 

 River. Some 65 million people live in the 300,000- 

 square-mile Mekong River Basin, also home to a 

 diverse freshwater fauna. 



he banks Of the Mekong River in Vientiane, the capital of Laos, 

 can be a lovely retreat at sunset. The river sweeps alongside the 

 city in a wide elbow curve, offering a panoramic view of tran- 

 quil waters and tree-lined shores. Thailand rests on the opposite 

 bank, seeming farther away than its half-mile distance. And as 

 the setting sun lights the water ablaze, birds skim the surface, 

 and fish make themselves known with the occasional splash, making an 

 evening walk along the riverbank a pure delight. 



At the start of a recent visit to Vientiane, however, one of us (Sterling) 

 wound her way through the city to the river, anticipating a cool breeze and 

 a quiet walk after a sweltering workday, only to stare into a scene from the 

 desert. Clouds of dust rose from the riverbed, where a group of kids were play- 

 ing soccer. Beyond that 

 bone-dry sandbar, a ves- 

 tige of the river was just 

 visible as a thin stream 

 along the tar bank. By all 

 appearances, one could 

 easily have walked across 

 to Thailand. 



Such radical fluctua- 

 tions are natural to the 

 Mekong, and whole 

 communities — human 

 and wild — are adapted 

 to its periodic floods 

 and droughts. The river 

 swells when rainfall 

 rushes down its tribu- 

 taries and shrinks again 

 in drier weather. But 

 the rise and fall of the 

 Mekong is increasingly 

 dictated by energy use 

 in China and Thailand. 

 Upriver hydroelectric 

 dams dampen the fluc- 

 tuations and change the 

 timing of floods and 

 dry spells, affecting wa- 

 ter-dependent wildlife 

 hundreds of miles away. The extent of those changes is likely to grow as 

 more dams, scheduled for construction, make their mark on the river. 



The dams are just one of the many troubles that confront the river and 

 its denizens; water extractions, pollution, invasive species, and overfishing 

 also threaten the ecosystem's health. And the Mekong's woes mirror those 

 of freshwater systems worldwide, which are increasingly pressured by a 

 growing human population that makes ever-greater water demands. The 

 scale is enormous: people now appropriate more than half of the world's 

 accessible surface freshwater, leaving precious little for natural svsteins 

 and other species to thrive. 



As a result, even as the human population of the globe has doubled, many 

 species that depend on freshwater ecosystems have suffered steep declines. 

 The list would bring tears to a conservationist's eyes: in the past three 

 decades, a fifth of the world's water birds, a third of freshwater mammals, 



I — 1 Mekong 

 — River Basin 



November 2007 natural history 



■ 1 1 



