The Yellow River valley in northern China is known as the cradle of Chinese civilisation.
It's what the Nile is to ancient Egypt, the Tigris and Euphrates to the Babylonians.
Millions of farmers might be forced to migrate
This is where the Chinese first learned to till and irrigate the land and where porcelain was first made 1,000 years before its "invention" in Europe.
It's not really a valley at all, more a vast expanse of plains and mountains stretching for 2,000km from the river's source high on the edge of the Tibetan plateau, to its mouth on the Yellow Sea.
Along the river's banks live a third of China's enormous population, more than 400 million people.
The vast plains that are irrigated by its muddy waters produce most of China's wheat, much of its maize and even some of its rice.
The Yellow River is also known as "China's sorrow". The name comes from its propensity to run wild, regularly inundating large swathes of the North China plain, and drowning tens of thousands of its inhabitants.
Overused and abused
But today the Yellow River is more famous for the exact opposite.
For more than 200 days of the year this once mighty river no longer makes it to the sea.
It's like the Rhine petering out in central Germany, or the Nile drying up in northern Sudan.
Why? In large part humans are to blame, in particular China's communist rulers, who have long believed nature should be bent to man's will.
The river has been overused and abused. Dozens of dams block its flow, drawing off huge quantities of water to grow cotton in the desert.
In 50 years the communists have done more to destroy the river than their predecessors in the last 5,000.
Today the whole region teeters on the edge of disaster. Global warming could push it over the edge.
In the next 50 years temperatures in Northern China are expected to rise by 3 to 4C.
As they do, the already arid climate will dry further.
The drought that has afflicted the region for the last six years would become permanent. The whole Yellow River valley will dry up.
The impact on crops would be dramatic. Scientists predict yields in China's main wheat growing region could fall by 20% to 40%.
This would force China to import huge quantities of wheat, maize and even rice.
But worse will be the effect upon those who live along the river.
Some are now predicting the creation of a dustbowl that would dwarf that of the American mid-west during the 1930s.
Economic policy has contributed to the river's decline
That forced hundreds of thousands of Americans farmers off the land in a mass migration to California.
But in China the effect would be much worse.
Literally tens of millions of farmers could be pushed off the land, and China has no California for them to move to.
Instead they would flood in to the cities, further swelling the ranks of the unemployed and dispossessed.
For China's leaders, it's a frightening prospect.