By Rupert Wingfield-Hayes BBC correspondent on the shores of Dongting Lake

Sitting on one of the huge dykes that surround Dongting Lake looking out across the enormous expanse of water, it is easy to forget that an epic struggle is under way.

The sun shines and the placid waters lap on the banks below. Sampans drift across the horizon.

We have to protect our homes and villages... We do this every flood season, although it is not always this bad

Villager

To be reminded of the danger, one has to turn around and look the other way, at the land on the other side of the dyke, often five or even 10 metres below the water lapping gently on the other side.

This is not like the floods in Europe with their huge swirling torrents of water surging their way across the continent.

Dongting Lake is more like a giant water-filled balloon that has been filled and filled until it is ready to pop.

All it needs is a tiny weakness, a pin-prick for its waters to come raging out across the surrounding land.

And so the struggle to hold back the waters continues day and night.

Repeated problem

Sometimes there is drama, when water is spotted trickling through a tiny hole.

The struggle to hold back the waters continues day and night

Villagers and soldiers then rush to the spot, filling sandbags and piling on gravel and rocks to plug the hole and stop it from growing into a full-scale breach.

But most of the time there is little drama - just constant vigilance.

Villagers in line abreast pace slowly along the high earth banks, their eyes cast downwards searching for any sign of a crack or a leak.

Atop the dykes, at 100 metre intervals, others sprawl under canvas tents keeping up their 24-hour vigil.

The heat is stupefying, but no one complains.

"We're used to this," one villager told me as he filled sandbags and piled them onto a truck.

"We have to protect our homes and villages. We do this every flood season, although it is not always this bad."

And that is the simple truth: floods are nothing new to the people here - they are a part of the cycle of life.

Higher walls

The reason is simple also, even if the solution is not. In China there are too many people competing for too little land.

As the population pressure has grown, more and more land has been stolen from the lakes

Good, flat, fertile land is scarce. And most of it lies along rivers and valleys and on flood plains.

For centuries, China has fought to control its rivers and lakes - to hold them back behind high flood walls so the land can be cultivated.

And in the last half century, as the population pressure has grown, more and more land has been stolen from the lakes themselves.

Dongting Lake may be vast, but today it is only half the size it was 50 years ago.

It is little wonder that when China's mighty rivers go into flood they have to be held back behind higher and higher walls.