THE greatest of all South-East Asia’s waterways and the world’s 12th-longest river, the Mekong, is a natural wonder that ties together the destinies of half a dozen countries. Born from snowmelt at over 17,000 feet (5,200 metres), it bolts off the Tibetan plateau like a runaway horse; by the time it leaves China it is starting to slow and spread. When it reaches Cambodia, via Laos, it is tropical and ample and, with the monsoon rains, parts of it curiously change the direction of their flow. Farther down, it reaches the South China Sea through a filigree delta. The Mekong watershed nurtures extraordinary biodiversity, with new species of plants and animals discovered every year. It has also nurtured humans. Tens of millions of people—much of the population of Laos, Cambodia, Thailand and Vietnam—depend on the Mekong. Its fish are their protein and its delta is the world’s rice basket. No wonder its name, in Thai or Lao, means “mother of rivers”.

Planners think the mother has one more gift to give: hydropower. China has 14 dams planned or under construction on its stretch of the Mekong in Yunnan province, joining six already built. Today the river is undammed below China, but that will soon change. Laos has nine dams planned or under way; Cambodia has two. Dozens more dams for tributaries are on the drawing board.

To the planners, the case for building dams is obvious: they generate electricity and much-needed cash. Poor, landlocked Laos wants to become the dynamo of South-East Asia, selling its energy to Thailand and others; it dreams of hydropower becoming its biggest earner in just a decade. Long wretchedly poor, the Mekong region is now booming. Hydropower will help meet its energy demands, which are expected to double over the next ten years.

Yet there are flaws in the planners’ case. For one, they overestimate the river’s potential. At most, says the Mekong River Commission (MRC), the intergovernmental body charged with co-ordinating the river’s management, dams will meet just 8% of the lower Mekong basin’s projected power needs.

Worse, the planners underestimate the harm that dams will do to ecosystems as well as to food security. As our essay on the Mekong points out (see article), dams threaten the stocks of migratory fish on which many South-East Asians depend. Farmland will either become less productive because less sediment reaches it from upstream, or disappear under rising river levels or, in the delta, suffer incursions of salt water. The dams, in other words, come at a high environmental cost, imperil food security and, far from increasing overall prosperity, promise to aggravate the poverty of millions of people. They may also increase regional tensions. China and Laos will reap most of the hydropower benefits, while downstream Cambodia and Vietnam pay most of the price.

The biggest problem with the dam-building schemes is their lack of co-ordination. An individual dam, high up the river system, would not be a big worry, especially if it was fitted with ladders for migrating fish and the like. But the question is not what one dam will do. It is what 25 of them will do, and how each will affect the next. The dams’ sponsors are not thinking about that.

Just keep it rollin’ along

Isn’t this the MRC’s task? Well, yes, and it tries to do its job. But it has no enforcement power, struggles to promote good river management and is woefully short of cash. Besides, China, the Mekong’s biggest threat, refuses to be a member. The MRC proposes a ten-year moratorium on dam-building, and has urged studies of hydropower projects, such as run-of-the-river schemes, that would not block the Mekong’s flow. That is prudent advice; but few governments are listening. The scale of the harm that damming the Mekong might cause is huge, and would be irreversible. Without giving enough thought to what they are about to undertake, governments are messing dangerously with the mother of all rivers.