The narrow street sloping up from the Yangtze river in the city of Fuling is lined with storage sheds, and crowded with people. Coal trucks grind upwards from the wharves and peasants hurry downhill with fruit-laden shoulder panniers, turning sideways to let the traffic pass. The road eventually becomes a long street of little shops. Walking up it - out of breath now - I see beside a dress shop with two life-size mannequins at the door, a large red sign proclaiming "177 m".
This, like the mark of the plague in medieval times, is a portent of doom. For everything below it, banks, shops, silk factories, roads, homes, wharves, storage cellars and stone steps cut from solid rock, is to be flooded when the Yangtze rises 177 metres above sea level on completion of the massive dam now under construction at the Three Gorges downstream.
Their fate will be sealed late this afternoon, when the mighty river is diverted at the dam site so that engineers can begin pouring concrete for the tremendous walls. The Yangtze will then start its slow rise to form a slender 600-kilometre (373-mile) lake, inundating an area the size of the Isle of Man, by the year 2006.
The dam is being built to end centuries of flooding in the lower reaches and to provide a clean new source of electricity. But all along the Yangtze, where the traffic of barges, sampans, junks, ferries, steamers and multistorey pleasure craft (complete with karaoke bars) is so heavy that it is called China's "main street", whole cities will be consigned to a waterworld to bring this about.
On a five-day voyage down the river last week from subtropical Chongqing, China's biggest city, with a group of officials from Beijing, I came across similar red notices everywhere indicating where the water level will be at different stages of the process.
Looking back downhill from the notice beside the dress shop, the enormity of what is happening becomes clear. It is as if the Irish Sea were to rise slowly over Dublin and everything had to be levelled as far as O'Connell Street. Here factories with tall chimneys will be blown so as not to become shipping hazards, streets will be bulldozed, power cables cut, lift shafts dismantled, drains filled in, oil sumps emptied, rubbish trucked away, and new wharves and promenades constructed.
There are years of work involved. Wang Shengun, director of a 10-storey candy factory which will be fully submerged by 2003, said that the machinery, window glass, tiles, toilets and furniture would be removed for recycling.
As the water comes up, all sorts of problems will occur. River rats for example, the main infection source of leptospirosis and endemic haemorrhage fever along the Yangtze, will move up and swell the rat population on higher ground so that "the source of plague will possibly increase for a short period," as a report by the Chinese Academy of Sciences puts it.
Over 1.2 million people will have to be resettled, the largest peacetime relocation in history. More than 50,000 have already moved to new homes on higher ground, but some peasants, like Li Hongying, 70 years old and with long grey hair and protruding teeth, still dwell in condemned family homes. Her house is in San Tan (Three Shoals), a village nestling among tangerine groves where we moored one afternoon.
"My family has lived here over 100 years," she said sadly. She was talking in the stone-flagged kitchen of the building with overhanging eaves (connected in rural Chinese fashion to an outhouse with the lavatory over a trough so that pigs can eat the human "night soil"). "The old can stay until the water comes. It will reach the door in 2003. Then I'll have to go." Her two sons have moved uphill to a line of modern two-storey houses built for them beyond a concrete headstone which marks the 177-metre limit. Many villagers refused to go at first but they soon left so as not to lose out in the redistribution of land. They grumbled about the thinner soil and the resentment of "uplanders" at the intrusion, and some complained they had got only 0.15 acres instead of the 0.27 promised, but they seem to have been treated well.
Their lives have certainly been disrupted less than people from Dongting further downriver who have been moved to Guihua Migration New Village, an hour's drive through sweeping mountain valleys. It is a single street of two-story houses in the middle of nowhere. Above them, once-barren hilltops have been terraced with dry-stone walls to create hundreds of sweet-potato plots. But they have no tangerines, the most valuable riverside crop.
"They gave us 15,000 yuan compensation for our old house but the new house cost 60,000 yuan and we had to borrow money from our relatives," said a shopkeeper. "The native peasants believe these mountains belong to them," he added, though a local man playing cards in a farm house said he sympathised with the plight of the immigrants. The peasants of Dongting were better off again than the "unofficial" coal miners of the Yangtze. I came across a handful of them, stripped to the waist and covered with coal dust, working a small seam just above the muddy beach. Every day they mine 10 tons of coal, pushing wagons of dusty slack along rails and tipping them out for collection by the coal barges which ply the Yangtze. "The water will swamp the shaft, and we will get no compensation," one told me.
The water will also submerge the big state-run mines at Fengjie, the ancient capital of the state of Kui, which we reached on the third day. From the deck we could see massive pits of fine coal along the bank, all destined to pollute the already filthy water of the Yangtze. Environmentalists worry that the dam will trap tons of silt, raw sewage and pollutants such as phenols and mercury, turning the reservoir into a toxic soup. A generation ago the water, now milk-chocolate brown, used to be crystal-clear, according to a ship's captain, but since then the factory waste, fertilisers and modern detritus had killed off most of the fish life. From the canteen window of his own steamer, the waitresses casually tossed empty plastic water bottles, one by one, through the window into the darkness every evening after we had finished dinner.
Many peasants mourn not just the loss of ancestral land, but the flooding of cultural relics. Some 172 kilometres (107 miles) downstream from Chongqing, in the city of Fengdu, known as the "City of Ghosts", fine Ming Dynasty walls will be lost when 30 square kilometres of the old town are flooded. Legend has it that the spirits of the dead come to this home of the Chinese divine comedy.
A group of Australian tourists entering the underworld shrines were unaware that the number "158" by the gate signified an intermediate stage of the coming apocalypse which will make Fengdu a real, underwater, ghost-town.
Long-term residents have mixed feelings about the future. Retired teacher Liu Zhu Guo, dressed elegantly in blue Mao jacket, said: "The distribution of new houses hasn't been announced yet, but I'm happy enough to go, the housing here is not very good."
An antiques dealer remarked: "Of course we're unhappy but if we don't move we'll be forced to move." His neighbour, Zhu Xiao Rong (73), whose husband fought in the Korean war, said with the weary fatalism of most river people that she was sad to leave her home of 40 years but would do what her work unit told her.
This means moving to a bleak new town we visited, composed of concrete apartment buildings, clad - like most new Chinese rural buildings - with shiny white tiles. The Beijing government, anxious to show compassion to the inhabitants of the 73 towns and villages moved back from the river and the 67 to be completely relocated, has pledged that almost half of the 240 billion yuan (£20 billion) cost of the dam project will go to compensate residents and to build new roads and power lines.
Officials build new schools first - we saw some modern classrooms full of children in the new towns - and close old ones so that parents will be encouraged to move. Big east-coast companies are being asked to set up factories in the region to absorb refugees. The money-making Wahaha bottling company has just opened a new plant - plastered with the ubiquitous white tiles - near Fuling and hired 1,300 workers from three condemned factories. "To aid the Three Gorges is not only our honoured task but our political task," said Wang Jhijian, the general manager.
Rounding a bend as we steamed down-river, the popular Zhang Fei Temple came into view. It clings to a cliff, but not high enough to escape the deluge. Chinese tourists arrive daily in cruise ships and coolies carry elderly visitors up to the shrine on pink sedan chairs. I met there Professor Lu Zhou of Tsinghua University who told me all was not lost. He has been put in charge of the relocation of the third-century shrine."It will be moved stone by stone," he said. Even a twisted old banyan tree growing through flagstones will be transplanted.
"The main problem is finding a site with the exact same topography," he added, as we strolled through the temple's Helpful Wind Pavilion, but just that morning he thought he had found the right place 30 kilometres upriver. The wooden beams and roof tiles might crumble when dismantled but they could be replaced, he said.
The temple, which commemorates a famous general of the Shu Kingdom (221-263), was already rebuilt twice in recent times, once in 1877 after a huge flood, and then again after it was wrecked in the Cultural Revolution. Lu Zhou's problems pale into insignificance compared with those facing Zhou Zinhua, mayor of the nearby city of Wanxian, where hills are so steep that bicycles are a rarity. Over 571,000 people, half the town's population, will have to move, he told us. A third of the Ming dynasty city, including 175 cultural relics, 900 factories and 597 kilometres of roads, will go under.
"We have the heaviest burden of resettlement," said the bespectacled Zhou. "This is the only city in the world ever to face such a task." As compensation, Wanxian is getting long-overdue funds for new roads and suspension bridges over the Yangtze, and a cascade of investment money has been promised. In Wanxian, too, the red signs daily remind people of their fate. One indicating the 146-metre second stage level, has been erected in Two Horse Street at the foot of a long pedestrian stairway with shops on each side. Watchmaker Chen Youling said dryly in his workshop, where he spent 20 years building his reputation: "I will be relocated according to a government plan."
Our ship at last reached the Three Gorges, where the current runs so fast that barges pass downstream like speedboats. It was night time when we entered the last one, the Xiling Gorge. Suddenly around a bend the darkness gave way to blazing lights, and the silence of the river was shattered by the noise of construction as we came upon the dam site and passed through the steep concrete walls of a diversion canal.
We left the steamer near Yichang, which the construction has transformed into a boom-town. It is connected to the dam by a fast new highway cut through the mountains. The city is known for its blind fortune-tellers, who carry little fold-up chairs for quick pavement consultations. Steel-helmeted police shooed them away when we tried to talk to them that evening.
Local officials were "cleaning up" the town in readiness for today's government ceremonies at the dam, a passerby said. Or perhaps they were just nervous about what the fortune tellers might reveal about the fate of China's gigantic gamble with nature.