Believe it or not, it was a Hong Kong-based explorer who discovered the definitive source of the Yangtze River, up on the Tibetan plateau. Wong How-man, president of the China Exploration and Research Society, last year headed a team that tracked the river back to a spot where it is little more than a large puddle in a wild region that is fiendishly difficult to get to. From that barren place, the Yangtze begins its 6,000km journey to the East China Sea, along a line that effectively marks the border between the northern and southern regions of the Middle Kingdom. The Yangtze waters spill into the ocean just outside Shanghai; the river that runs through the city, the Huangpu, is one of its many tributaries. The Yangtze is a key trade and transport route, as well as being a source of food for people living along its banks, irrigation for farmers and a convenient waste-dumping receptacle for irresponsible factory owners. It has also been the backdrop for politically motivated dramas; at the age of 73, Mao Zedong made a great display of taking a Yangtze dip to show how fit and healthy he was. Reports at the time said he had completed a 15km swim in just over an hour, an astonishingly fast pace for an elderly, overweight man. 'I had been swimming with Mao so many times before that I barely noticed the event,' recalls the dictator's personal doctor, Li Zhisui, in his memoir, The Private Life of Chairman Mao. 'Nor did it occur to me that foreign sceptics might gasp in disbelief that a 73-year-old man could swim faster and further than an Olympic champion. I knew how swiftly the Yangtze flows through Wuhan: Mao had only floated on his back, his giant belly buoying him like a balloon, carried down the river by the current.' It is not a view the doctor would have voiced at the time; torture and death were the well-established methods of dealing with doubters and dissenters. The 1966 stunt was clearly designed to demonstrate the Great Helmsman was in control and ready to launch the next bloody phase of his rule, the Cultural Revolution. In more recent years, the controversial Three Gorges dam project, which has displaced hundreds of thousands of villagers, has been hogging the headlines. And it is not the only aspect of the Yangtze that is changing. Little-publicised works are currently underway to link two outer-estuary islands with the mainland, which will create a massive deep-water container port. This project seems certain, in years to come, to make Shanghai the world's biggest and busiest container port. Most sources agree the Yangtze is the third longest river in the world, at 6,380km, after the Nile (6,695km) and Amazon (6,452km). Authenticating the precise spot where a river springs up, though, can be a disputatious business. The word of the Royal Geographical Society in London is generally reckoned to be final. It seems Wong's discovery, acknowledged by the society, is the last word on the Yangtze's source. His expedition utilised the latest satellite technology to pinpoint where the river begins ... before it flows past the spot of Mao's swim and all the way to Shanghai, the nation's largest city.