By Peter Greste
BBC News, Caia, Mozambique
From the air, the Zambezi valley looks more like an inland sea than the river it is.
Mozambique authorities are struggling to contain the disaster
Although the main channel is clear enough, with reeds lining the bank, the water now spreads almost as far as the eye can see.
The roofs of submerged mud huts dot the water like giant lilies, while fields of corn and sugar cane choke in rising water.
It is spectacular; but it is also deeply worrying to the authorities struggling to contain this slow-burning disaster.
The waters began rising weeks ago, when unseasonably heavy rains fell in the Zambezi's headwaters in Zambia and Zimbabwe.
In Mozambique, the broad, lazy river slowly began to rise. Soon, it trickled over its banks and into the villages closest to the river's edge.
Domingos Manuel and Joao Manteyro fled their homes and their fields along with the rest of the village.
They retreated to another community fortunate enough to live on slightly higher ground.
There, they built temporary grass huts on the ever-shrinking pocket of dry land.
"This is a disaster," Mr Manuel said. "We lost our crops and our farms in the floods last year. Now, it's happened again, and I don't know how we'll survive."
He and Mr Manteyro waded through the water, chest-high in places, to return to their homes to salvage a few precious possessions they could not carry in the first flight - a broken plastic bucket and a hoe.
"It's not much, but we have so little left that we can't leave anything. It will all be useful to us," Mr Manteyro said.
To outsiders, it makes no sense for these villagers to be on the flood plains.
The river now seems to burst its banks with monotonous and terrifying regularity.
"Where else can we go?" Mr Manuel asked with his hands in the air. "This place is our home. It gives us crops and fish. We don't know anywhere else."
And they are not alone.
After last year's floods, the Mozambique government set up resettlement camps, designed to give a more permanent home to those displaced by the river.
In all, about 100,000 people were forced to flee that year and a quarter of a million needed food aid.
But most of those displaced returned to their farms, preferring to risk another flood than surrender their dignity and independence.
Now though, the challenge for aid workers is to get to and help those caught once more by the rising flood.
The Mozambique navy is running search-and-rescue missions to evacuate those most at risk.
It has already helped more than 50,000 people to safety, and if the waters continue to rise as predicted, the navy may have to evacuate that many more again. But the task is enormous.
Mozambique's National Disaster Management Institute, which is co-ordinating the relief effort, only has one helicopter at its disposal - a five-seater that is fully occupied with planning and monitoring.
So the only alternative is by boat. But the flood plains are so shallow that it is almost impossible to get any boat big enough to evacuate large numbers to those who need rescuing.
Instead, the navy has a large barge on the main river channel, with small inflatable boats scouring the flooded villages for victims.
For the World Food Programme's director in Mozambique, Geronimo Tovela, ironically the crisis is not as bad as it might otherwise have been.
"We already placed significant stores of food in key areas as a part of our ongoing feeding programme from the 2007 floods," he said.
"That means their immediate needs are met. Of course we'll still need to bring in more, but it's not a panic."
Other agencies like Unicef are looking at some of the more pressing problems.
"We're concentrating our efforts on assessing the needs in the resettlement areas as the families are coming in," said Unicef's emergency co-ordinator for Mozambique, Lisa Doherty.
She said her agency was looking at water and sanitation facilities to prevent outbreaks of cholera, and providing malaria nets and other health supplies.
So what of the future? Forecasters say the rains are continuing to fall in Zambia, Zimbabwe and Malawi, and the run-off is pouring into the Zambezi River.
That flows into the massive Cahora Bassa dam in Mozambique's west, but the in-flows are far exceeding the amount they have been letting out.
The authorities warn that they will have to release more water, or risk having the dam burst.
It is also just the start of Mozambique's long wet season.
"The levels of water will continue to increase a lot, and the response from the humanitarian community is really just beginning now," Ms