The Three Gorges dam was so vast and sweeping a vision that nothing could stand in its way. Not the old cities of the Yangtze valley, storehouses of human toil and treasure for more than a thousand years. Not the lush, low-lying farmlands, nor the villages, nor even the pagodas and temples that graced the riverbanks.

The cries of dissenting scientists and the lamentations of more than a million Chinese people forced to leave their ancestral lands counted for nothing.

When the waters rose to 570ft last year, drowning all these things, it marked a triumph for the engineers at the top of the Chinese Communist party.

But in the past six months a sinister trail of events has unfolded from the dam all the way up the 410-mile reservoir to the metropolis of Chongqing.

It began with strange, small-scale earthquakes recorded by official monitoring stations and reported by the Chinese media.

Mysterious cracks split roads and sundered schoolhouses and apartments in newly built towns and villages on the bluffs looking down on the river.

The local government now says that 300,000 people will have to move out in addition to the 1.4m evicted to make way for the dam.

More than 50,000 residents have already been relocated owing to seismic problems that were not foreseen when the dam was built, according to the state news agency, Xinhua.

As the boats sail by, landslides can be seen from the river — some small, some big — staining the waters of the Yangtze with minerals and sediment.

Big pleasure cruisers, tramp steamers and shoals of sampans plough through waters that switch from hue to hue as their chemical composition changes.

In Badong county, midway through the Three Gorges, celebrated in Chinese painting and poetry, the citizens are troubled by a sense of foreboding.

The local government hastily moved out of a prestigious new block after experts warned that it was unsafe.

But ordinary folk and even schoolchildren have been left to fend for themselves. More than 3,000 children attend school every day in a building dating back to 1943 that officials know to be at risk of collapse. Nothing has been done to move them, supposedly because of a lack of funds.

The playground is riddled with cracks. One ominous jagged line runs down the side of the classrooms.

“The government agrees that our whole school must move,” said a worried teacher, who asked not to be named, “but so far it’s just talk.”

In a telling example of China’s glaring class differences, a group of unemployed workers live in housing provided by the state that is visibly cracking at the seams.

“What kind of dogshit government moves itself out and moves us into somewhere like this?” one of them complained.

“My house is like a fishing pond whenever it rains,” said Grandma Wang, 72. “I don’t mind for myself because I am old, but I care for my granddaughter, who is 10 and has to live in here.”

Badong is one of many places where the land and the water have interacted in ways that only a few scientists predicted before the dam was built. Their objections were overruled by the party.

But last week even the state media acknowledged that the Three Gorges area faced a “grim” situation. Officials have counted 97 significant landslides this year alone. These are linked to the worrying increase in seismic activity.

As the water rises, it penetrates fissures and seeps into soil. Then it loosens the slopes that ascend at steep angles on either side of the river. Eventually, rocks, soil and stone give way. The landslides undermine the geology of the area. That, in turn, sets off earth tremors. It may be the world’s biggest case of rising damp.

One of the most startling examples can be seen on the river at an ancient stopping point where sampans moor. Hundreds of migrant workers live in abandoned shops and small houses along “the steps to the sky”, a stone staircase ascending from the riverbank up which labourers still carry their burdens on poles. A spiderweb of cracks patterns the slope.

“The owners all moved out because they are scared, so we rent this place out to porters to sleep for 10 yuan [about £1] a night,” said a drink seller.

Nearby, two entire apartment buildings stand vacant with their windows and doors open to the rains. An official notice warns: “Dangerous Dwelling!”

The dam, built at a cost of more than £15 billion, was meant to control the scourge of flooding, irrigate arid provinces and generate millions of kilowatts in cheap, clean electricity. It is not working out like that.

As the summer rains build up and the waters rise again behind the breathtaking span of the dam, with its 26 mighty turbines, only a trickle of stagnant water emerges.

Along the waterfront in Yichang, the nearest city to the dam, people wash their cars in the water, but the smell can be overpowering.

“It’s not clean,” said the captain of a ferryboat chugging upstream on the reservoir. “I’ve been on the river for 30 years and in the old days the water was so swift that anything dirty was swept away. But now it’s a lake. The waters are still. All the filth sinks to the bottom.”

Once fast-flowing, the river seems oddly tranquil, and from the wharves at Chongqing it looks stagnant, polluted and murky.

Officials dismissed the first landslides as the foreseeable side-effects of a massive dam project. They are not so dismissive now. A total of 9,324 potentially dangerous sites have been identified. Geologists working midway down the reservoir have found 700 around one town alone on the north bank. Experts say the landslides could go on for 20 years as a huge settlement of earth and water takes shape.

It will cost China more than £5 billion to solve all this. A special budget is being worked out inside the opaque bureaucracy that controls the state’s megaprojects.

On the plus side, the power is flowing to cities as far away as Shanghai, and officials argue that it cuts air pollution and reduces greenhouse gases. They have built 50 waste water plants to cleanse the reservoir and created numerous landfill dumps.

However, political and scientific confusion reigns over the dam’s failure to relieve drought in the provinces of Hubei, Hunan and Jiangxi down the Yangtze, while leaders argue about how much water to release, and when.

“There are some good things and some bad things about the dam,” said Huang Lu, 64, an itinerant seller of cigarettes and sex potions along the river. “But we older people lost so much ... our memories, our friends, our culture. Now I can only see the old things in my dreams.”

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