Environment: Bulldozer triumphs as time runs out for the mighty Yangtze

China has taken the first steps towards diverting the course of the mighty Yangtze. Next month, the controversial Three Gorges Dam will reach the point of no return. Teresa Poole looks at a project criticised as an environmental disaster in the making.

It was nearly 80 years ago that the father of the Chinese republic, Sun Yat-sen, first proposed a dam across the Yangtze. But for the boatmen who work the river near the massive dam site in central Hubei province, this week marked the turning point.

Travelling by boat downstream towards the dam project, the majestic river starts to make a sweeping leftwards bend as one approaches China's biggest construction project since the Great Wall. Work started three years ago and since then the Yangtze boatmen have watched an army of peasants digging a canal to the right-hand side, part of the biggest earth-moving exercise in history. At the same time, a wall of concrete - the preliminary "coffer dam" - has slowly been inching its way across the river, slicing into the main stream and gradually re-routing this stately river into its new channel.

Two days ago, the boatmen were told that they could no longer travel along the route Mother Nature intended, and must instead swing out through the four-kilometre canal. Over the next four weeks, the gap in the coffer dam will slowly be closed across the original river, culminating in a ceremony early next month in which the final blocks will be put in place under the watchful eye of the dam's most powerful backer, the prime minister, Li Peng. Thus will the Yangtze be diverted by the might of the bulldozer.

With the natural riverbed then dry below the coffer dam, work will begin on building the real dam wall, a 175-metre curtain of concrete which will sweep between the hills on either side of the river. When the whole project is completed in 2009, the dam will have created a 663-km long snake-like reservoir which will flood an area twice the size of the Isle of Wight. The upstream river level will have risen 100 metres, and the famous Three Gorges scenery will be underwater.

For both opponents and champions of the project, the scale of the endeavour is breathtaking. By completion, some 103 million cubic metres of soil and rock will have been excavated. Most controversially, around 1.2 million people, 1,600 enterprises, several cities, 140 towns and 4,500 villages will have been relocated.

The Chinese government is putting its money where its mouth is: by the end of the year it will have spent 27 billion yuan (pounds 2bn), but this is nothing compared with the projected total cost of 203 billion yuan.

The questions which surround the project are as massive as its demand for cement. The human rights implications of the forced relocation is one major aspect of the project on which China has not encouraged foreign scrutiny. But there are less emotive issues that are just as worrying: the silt that will build up behind the dam, the threat to fish and fauna, and the submersion of archaeological relics.

For the Yangtze boatmen, the project is already a nuisance. If the river flow is too strong their boats will not be able safely to pass through the canal and will have to use a temporary ship-lock which will not be ready until next May. And during high flood season, navigation will be prohibited completely.