Dachaoshan is part of a multibillion-dollar effort by Beijing to develop its upstream half of the 4,840km waterway. China said the construction would lift backward southwestern provinces such as Yunnan, home to 43 million people, out of poverty. But critics warn Beijing has ignored potentially disastrous effects on farms and fisheries in the other five countries that share the Mekong – Vietnam, Thailand, Laos, Cambodia and Myanmar. “China acts like it doesn’t need to care about countries downstream. It has to recognise that the Mekong isn’t just theirs,” Witoon Permpongsachareon, director of Terra, a Bangkok-based environmental group, said.

The US$600 million (HK$4.6 billion) Dachaoshan is the second of at least eight hydroelectric dams Beijing wants to build on the region’s most important waterway over the next two decades. The first, at Manwan, was finished in 1993. Work is to begin next year on the Xiaowan dam, a US$4 billion structure the height of a 100-storey building that will be the world’s tallest dam. Plans also call for dynamiting a shipping channel through the Mekong’s extensive rapids, fulfilling Beijing’s dream of turning the river into a link to Southeast Asia’s export markets and raw materials. China has already cleared its own rocks and built two river ports at the cities of Jinghong and Simao in Yunnan.

In June, limited freight and passenger services opened to northern Laos and Myanmar. Next month, Premier Zhu Rongji would announce US$5 million in aid to Laos and Myanmar to blast a further 290km of rapids in those countries, Chinese officials said. They said the offer was proof that they were serious about promoting joint development. “All countries will prosper equally from the increased trade,” said Mei Ruichang, a spokesman for Yunnan’s Navigation Affairs Bureau, which is overseeing the river-clearing work.

But critics said China was ignoring fears in Laos that destroying the rapids might damage tourism, a big money-earner for the impoverished country. They also complain that Beijing refuses to join regional efforts such as the four-nation Mekong River Commission to co-ordinate development. Scepticism has also met Chinese claims that dam-building will benefit countries downstream. Beijing said the dams would ease the annual cycle of flooding and water shortages that accompanied rainy and dry seasons. But experts said that would spell disaster for critical fisheries, such as Cambodia’s Great Lake, the main source of protein for the country’s 12 million people. The lake depends on the yearly floods to replenish nutrients. Farmers in Laos also wait for the dry season to plant on the exposed river bottom’s fertile mud. Critics say the dams will block migration routes of rare species such as the giant freshwater catfish, which can weigh up to 290kg. The dams could also slow the river’s flow, raising water temperatures and possibly wiping out native fish species.

Chinese officials call these concerns exaggerated, although they admitted some environmental damage was inevitable. Still, they said, the dams were necessary to power Yunnan’s industrialisation and improve living conditions. In Shandi, a village about 1.6km uphill from Dachaoshan, the first electricity came two years ago. Lu Mingxie uses a single naked bulb to light her dirt-floor home as she shucks corn and peels dark green pumpkins. The 50-year-old farmer welcomes the progress. But she, too, has her complaints about the central Government’s high-handed way of bringing it about. Ms Lu said dam officials seized a one-third-hectare plot of good rice paddy near the dam that her family had farmed for six generations. They promised compensation, but she has yet to see any. “Not everything about this dam is good for us common people,” she said.