ISTANBUL (Reuters) - Countries that selfishly use shared rivers threaten political stability at a time when water is scarce and demand is growing, a conservation group warned on Wednesday.

A view shows the Tigris river in Baghdad February 11, 2009. REUTERS/Ahmed Jadallah

Disputes over shared rivers such as the Tigris and the Euphrates could be resolved if nations put borders aside and viewed the entire river basin as a unit instead, they added.

In the past some states have built dams or siphoned water from rivers for irrigation without consulting neighbors downstream -- stirring political tension.

“The question countries must face is are they interested only in holding all the water themselves and living in a destabilized region, or do they wish to share the water and cooperate?” said Mark Smith, head of the water program of the International Union for Conservation of Nature (IUCN), a body funded by states, and NGOs.

Rivers shared by more than one country provide about 60 percent of the world’s fresh water. There are 260 international river basins in the world, covering half of the Earth’s surface and home to 40 percent of the world’s population.

Traditionally the focus in negotiations over shared rivers has been how to apportion water. Once the water is divided each country tries to optimize water use within its borders, rather than across the shared basin, the IUCN said.

By working jointly countries could reap better economic benefits from rivers and ease political tensions.

Turkey, hosting the triennial World Water Forum in Istanbul, is home to the sources of the Euphrates and Tigris, which form a river basin flowing through Syria and Iraq before draining into the Gulf from Iraq. Wrangling over the rivers is longstanding.

Upriver dams built by Turkey, Syria and Iran have caused Iraq water shortages, exacerbated by an infrastructure devastated by war.

“There is a real distinction between the upstream and downstream position. Those upstream hold a lot of power. In Turkey that power is accentuated because Syria and Iraq are very dry countries,” said Smith.

Smith said some countries cooperate well, such as Guinea, Mali, Mauritania and Senegal which share the Senegal River, while the Volta river is shared by six West African states.

“The Rhine for example used to be a huge source of dispute between France, Germany and the Netherlands, particularly over pollution... institutions were set up and now the river is co-ordinated and is a clean river again.”

In states were huge dams have been built to the detriment of other nations downstream, the flows of the dams could be altered to allow rivers to replicate their previous natural patterns, Smith said, which would help restore ecosystems. Turkey been heavily criticized by some environmental groups during the conference for pursuing large scale dam and hydro-electric power building projects.

Most controversial is the 1.2 billion euro Ilisu project, begun in 2006, which will construct a dam on the Tigris river, bury part of the ancient town of Hasankeyf and force the relocation of thousands of people.