Thousands of people are encamped with their farm animals on tiny strips of land surrounded by floodwaters in Battambang province in northwestern Cambodia.
John Macgregor, an aid worker who has been accompanying teams delivering food and water to Battambang, described the area as a vast inland sea where conditions are dire and malnutrition is common.
"Diseases are becoming more common and yesterday our doctors diagnosed the first cases of cholera. People are sleeping in extended family groups on rush mats which sit on the mud, under strips of clear plastic. Ducks, chickens, dogs and cats are often in there with people - a factor in the mounting disease toll," said Macgregor, communications director of Cambodian War Amputees Rehabilitation Society (CWARS) from Phom Penh, the Cambodian capital.
CWARS delivered food to 6,000 people and its medical teams treated 1,600 patients in seven days.
"We drove for six hours – the roads are wrecked from rain – then waded through floodwater for half an hour, then got a boat for about an hour," Macgregor said. "Much of northern Cambodia has become a vast inland sea – an astonishing sight. We travelled by boat for an hour at a time between bits of dry land."
Like other countries in the region, Cambodia has been hit by heavy monsoon rains that have overwhelmed swollen rivers, dams and canals, causing the worst flooding in decades. It is estimated that 250,000 people in the three worst-affected provinces are inundated and without aid.
According to the UN, more than 20 provinces in Thailand – one third of the country – are under water. Twelve provinces are on high alert, including Bangkok, and around 2.4 million people have been affected countrywide; 700,000 are estimated to be children. In Cambodia, 17 out of 23 provinces continue to be flooded while 250,000 people have been affected in Vietnam. Half a million people have been affected in Laos, with damage to more than 64,000 hectares (158,000 acres) of farmland, while 254,400 people in the Philippines have felt the brunt of a series of typhoons.
Many flood victims have been children. In Vietnam's Mekong delta, 49 of the 57 deaths since August have been children, according to the national flood and storms control department. In Cambodia, at least 80 children have died, while more than 50 have been killed in Thailand, all mostly from drowning, according to the UN.
In Battambang, Macgregor saw a canoe carrying three children overturn. "They started to drown. The villagers, who couldn't swim, threw them some of our empty water containers and they were saved," he said.
Children have made up around a quarter of the nearly 800 deaths reported since July across Thailand, Cambodia, Vietnam, Laos and the Philippines, according to the UN. Every year, an estimated 240,000 children aged up to 17 die mostly because they have never learned to swim.
That annual number is roughly equal to the total deaths from the 2004 Indian Ocean tsunami, but day-to-day water deaths attract little attention.
The floods have also taken a heavy economic toll: in addition to the damage to Thailand's rice crop, the market is concerned about typhoons hitting production in the Philippines, the world's biggest importer until last year, and seasonal floods in Vietnam's Mekong delta.