By Michael Bristow
BBC News, Beijing
There are fears that China's Three Gorges Dam is causing serious environmental problems, despite official claims to the contrary.
The dam is meant to alleviate flooding and generate electricity
Local farmers, environmental campaigners and even officials themselves have voiced concern about environmental damage.
That damage includes landslides that have triggered 50 metre-high waves on the reservoir behind the dam, according to one local official.
But despite these widespread accusations, the Chinese central government insists there are no geological "abnormalities".
Critics of the Three Gorges Dam - the world's largest hydro-electricity project - have long argued that the scheme would lead to environmental problems in the area around the reservoir.
In September, those fears appeared to be confirmed when speakers at a government-organised conference warned of "environmental catastrophe".
They said there had been more frequent natural disasters, severe erosion, landslides and ecological degradation since the dam was constructed, according to state media reports.
And those making the comments are in a position to know - many are officials who are directly connected to the project.
Wang Xiaofeng, deputy director of the government's Three Gorges Project Construction Committee, told conference delegates: "[We cannot] profit from a fleeting economic boom at the cost of sacrificing the environment."
Tan Qiwei, vice-mayor of Chongqing, a municipality next to the reservoir, said the lake's banks had collapsed in 91 places.
These landslides are being caused by the huge weight of water behind the dam and fluctuations in the water level, delegates at the conference were told.
Farmers living near the dam's reservoir, which is 660 km (410 miles) long and an average of 1.1 km wide, tell a similar story.
They talk of frightening tremors since the dam was completed last year, that have left cracks in the walls of their homes.
Four million more residents than planned will have to be relocated
Last week, a landslide in Badong County in Hubei Province, alongside the reservoir, killed more than 30 people after burying a bus.
Chongqing officials recently announced that four million more residents would have to be relocated to "protect the ecology of the reservoir area", according to state media reports.
The project's initial plan had been to move just 1.2 million people.
But despite these developments, China now insists that there have been no unforeseen environmental problems related to the project, due for completion in 2009.
Wang Xiaofeng, the official who in September had seemed to warn of catastrophe, this week took a different line.
"Geological disasters in this area have been effectively controlled," he said at a press conference in Beijing to discuss the environmental impact of the Three Gorges Dam.
Although he did not discount the possibility of natural disasters in the future, he added: "There will not be any major damage to life or property."
He also rebutted the various accusations claiming the Yangtze River dam is causing environmental damage.
Mr Wang said there was less than half the expected levels of silt behind the dam, and outbreaks of algae in waterways feeding into the reservoir had been controlled.
Rare floral and fauna had been protected, he went on, and there was only a low risk of reservoir-induced earthquakes.
Mr Wang also denied that the issue of four million extra residents being moved from their rural homes in Chongqing was anything to do with the $24 bn (£11.7 bn) Three Gorges Dam.
Banks of the Yangtze are being reinforced to prevent landslides
And he added that the project was achieving its intended aims - to produce clean electricity, to control flooding and to improve shipping along the Yangtze.
Who to believe?
So with so much conflicting evidence, who is telling the truth?
Chinese writer Dai Qing, who has long campaigned against the Three Gorges project, is in no doubt.
She says there is environmental damage and the government is trying to cover it up.
"If they're saying that the landslides have nothing to with the reservoir than they are telling lies," she told the BBC.
The activist said the area was unstable before construction began, and was never a suitable site to build such a large dam.
"They're not truthfully reflecting a serious situation. The government is not being responsible to business or to China," she added.
THE THREE GORGES DAM
Type: Concrete Gravity Dam
Cost: Official cost $25bn - actual cost believed to be much higher
Work began: 1993
Due for completion: 2009
Power generation: 26 turbines on left and right sides of dam. Six underground turbines planned for 2010
Power capacity: 18,000 megawatts
Reservoir: 660km long, submerging 632 sq km of land. When fully flooded, water will be 175m above sea level
Navigation: Two-way lock system became operational in 2004. One-step ship elevator due to open in 2009.