Enviroment: River may become the world's biggest open sewer

The Ecology

The Yangtze is the third longest river in the world, rising in Tibet and emptying into the sea near Shanghai some 4,000 miles later. Its opaque waters run thick with sediment; every year the river carries down some 530 million tonnes of silt, and this poses the biggest long- term environmental and technical problem.

Once the reservoir has been created, the flow of water upstream of the dam will be much slower, and more of the silt will therefore be dumped on the river bed. Critics forecast, for instance, that after a few decades the proposed deep-water harbour at Chongqing city, at the top end of the reservoir, will be clogged by the silt. The 375-mile long semi-stationary reservoir waters will also be polluted by a steady build-up of huge quantities of raw sewage and factory pollutants which already empty into the Yangtze.

One Chinese environmentalist privately described the likely result as "the biggest open sewer in the world". Large quantities of silt will also build up behind the main dam wall itself.

Given the scale of the project, environmental concerns span a number of issues. The most alarming warning is that the weight of the huge volume of water in the reservoir could promote seismic activity in the area. Separately, landslides along the unstable banks of the Yangtze are already common and preventative measures will be needed around the dam site itself.

Disruption to the natural flow of the river threatens a number of rare plant and animal species, including the endangered Yangtze river dolphin. Downstream lakes and wetlands will also be affected. Around 1,300 sites of historical and archeological interest are destined for a submerged future, with only the most high-profile sites likely to be rescued in time.

On the plus side, hydro-electric power is much cleaner than the dirty coal-fired power stations used to produce more than three-quarters of China's electricity.