China’s 1.3 billion people are already short of supplies because of prolonged drought in many regions — and much of what remains has been contaminated by industrialisation.About 40 per cent of all waste water produced in China — some 25 billion tonnes per annum — flows into the river, but more than 80 per cent of it is untreated beforehand.

Companies are lining up to bid for contracts to build the biggest public works project in human history: a canal that would divert water from the Yangtze river to the Northern plains of China.

The Chinese government has sparked artificial snowfall in Tibet, which could alleviate the region’s draught, and help feed the rivers that start in the Himalayas.