UN study advises caution over dams

China is constructing a series of eight dams on the upper half of the Mekong as it passes through high gorges of Yunnan Province, including the recently completed Xiowan Dam, which - at 958 feet (292 meters) high - is the world's tallest. Its storage capacity is equal to all the Southeast Asia reservoirs combined, the U.N. report said.

Laos, meanwhile, has started construction on 23 dams expected to be finished by 2010 on the Mekong and its tributaries, the U.N. said, as a means to spur development and lift the country from poverty. Cambodia and Vietnam also have ambitious dam-building plans.

"China's extremely ambitious plan to build a massive cascade of eight dams on the upper half of the Mekong River, as it tumbles through the high gorges of Yunnan Province, may pose the single greatest threat to the river," the report said.

The report went onto to say that the impacts of the proposed dam development include "changes in river flow volume and timing, water quality deterioration and loss of biodiversity."

China's Foreign Ministry spokesman Ma Zhaoxu said in a regular briefing the government pays equal attention to the development of the Mekong and its protection. The Mekong is known as the Lancang river in China.

"I would like to point out that the Chinese government attaches great importance to the exploration and the protection of cross-border rivers and conducts the policy of equal attention to development and protection," Ma said.

The proposed dams would add further pressure to the Mekong, which runs through China, Myanmar, Laos, Thailand, Cambodia and Vietnam. The 307,000-square-mile (795,000-square-kilometer) river network is home to dozens of rare bird and marine species, including the Mekong giant catfish, and is a source of food and jobs for the 65 million people who live in the river basin.

The river and its vast tributary network already face threats from pollution, climate change and the effects of earlier dams that were built in China and have caused water levels to drop sharply on the upper Mekong.

Still, the U.N. report said for the time being, the Mekong's pollution levels were not at "alarming levels" while water shortages and conflicts over water on the Mekong have so far not emerged.

"The Mekong is in good condition at this time and can take more pressure such as irrigation development or industrial development," said Mukand S. Babel, one of the reports' authors.

The report, however, found several river basins in the Mekong that are under threat, including the Tonle Sap in Cambodia, Nam Khan in Laos and Sekong-Sesan Srepok in Vietnam and Cambodia due to increasing development and demand for water.

It called for countries bordering the Mekong to work more closely together to ensure that the region's growing population and expected economic development doesn't further strain the capacity of the delta.

"The time to tackle these challenges is now, otherwise the projected growth and development may impact on the basin's ability to meet future water needs," said Young-Woo Park, a U.N. regional director.

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