Fresh water supplies in countries hit by the Asian tsunami are under serious threat, according to a UN report.
Groundwater supplies are now contaminated, says the study
Drinking water sources have been contaminated by salt water and sewage, and every well in Sri Lanka may have been affected, the study says.
Hazardous materials such as toxic waste and asbestos from buildings may also be in the water in some areas, it adds.
The study is the first attempt to assess of the environmental damage caused by the 26 December disaster.
"Shallow wells and groundwater supplies, especially in small islands, are now contaminated with salt water," says the study carried out in Indonesia, the Maldives, the Seychelles, Somalia, Sri Lanka, Thailand and Yemen.
Agricultural land has also been damaged by salt water, which the study says will affect crops in the short term.
The UN Environment Programme (Unep) report states that about 250,000 people died in the tsunami which it describes as "among the worst human tragedies in history".
By contrast, wildlife is said to have fared well in general, but from Sri Lanka come reports of turtles being eaten in substantial numbers owing to a lack of fish, and in the Seychelles the tsunami ripped up beaches where turtles nest.
In addition, tens of thousands of fishing nets have been swept out to sea where they remain a potential threat to fish, birds and mammals.
The report says there is evidence that where coral reefs, mangrove swamps and vegetative sand dunes had remained intact, the tsunami caused less damage.
The UN says that preserving these natural defences should be a priority.