Turkey, which will host the next forum in March 2009, was taking over the chairmanship of the conference from Mexico, which held the forum last year.
On Monday, the conservation group World Wide Fund for Nature issued a report warning that pollution, dams and climate change could destroy some of the world's most important rivers in coming decades, causing severe water shortages and the extinction of a number of fish and other species.
About 300 delegates in Istanbul were working on an agenda that is expected to focus on ways to improve management of water resources and improve communication between developed and developing regions, the organizers said.
Iraq and Syria have often accused Turkey of holding back too much water in dams on the Euphrates and Tigris rivers, an allegation Turkey denies.
In its report on Monday, WWF urged governments to step up efforts to preserve rivers, lakes and wetlands that provide millions of people with drinking water and food, and the water needed for agriculture.
It said only 21 of the planet's 177 longest rivers run freely from source to sea, and dams and other forms of human construction destroy the habitats for migratory fish and other species by altering the water's natural ebb and flow.
WWF's report focused on 10 rivers: Europe's Danube, North America's Rio Grande, South America's La Plata, Africa's Nile, Australia's Murray-Darling, and Asia's Yangtze, Mekong, Salween, and Ganges.
More and more water is needed to meet the needs of rising populations in towns and cities near rivers, and global warming is expected to have a significant impact on fisheries in places such as Africa, where even small changes in temperature can dramatically alter water levels and fish productivity.
