WASHINGTON –

There's one thing Islamic State militants and the Iraqi government they're besieging agree on: Turkey is using more than its fair share of water.

Water levels on the Euphrates River that flows 2,700 km (1,700 miles) from eastern Turkey through Syria and Iraq past ancient Mesopotamian lands have fallen more than half this year, withering farmers' crops and raising the risk of a wider regional conflict, Iraqi officials say.

Iraq and Islamic State say Turkey needs to release more water from its dams to replenish the river in the former Fertile Crescent area where drought-like conditions endanger millions. The situation has grown even more acute for Iraq after Islamic State, whose holdings fall within the watershed, used a dam captured in Ramadi in June to cut off water to government areas.

Turkey, for its part, says it has to look after its own and is investing $35.5 billion in dam and irrigation works to ensure reliable water supplies.

The problem in the region is not "which country to blame," said Jay Famiglietti, a NASA water scientist. "It is really over the failure to agree on how to manage the waters of the rivers across political boundaries."

Turkey acted unilaterally to build the dams and "has significantly changed the amount of river flow to downstream countries like Syria," the hydrologist said by email.

Construction is underway on the last six dams of a 22-dam project in southeastern Turkey, mostly on the Euphrates and Tigris, which flows south from Turkey, making part of its border with Syria before crossing the length of Iraq. Dam and irrigation projects on the Tigris — the first to tap the waterway — are due for completion next year despite Iraqi protests.

Turkey signed an accord with Syria in 1987 to keep about a third of the Euphrates historic average flow, according to the Food and Agriculture Organization. It has no such treaty with Iraq.

No international agreement for the Tigris existsl A Turkish official, speaking on condition of anonymity because of the sensitivity of the subject, said Turkey could be persuaded to regulate the Tigris' flow at a similar rate as the Euphrates.

Still, "Turkey's desire to withdraw yet more water runs the risk of plunging the region into greater turmoil," said Adel Darwish, co-author of Water Wars: Coming Conflicts in the Middle East. "Turkey believes it can act with impunity while other countries are busy fighting Islamic State."

Lacking "a basin-wide international agreement is certainly an obstacle" though there are bilateral arrangements on sharing of water between Turkey and Syria and Syria and Iraq, said Vakur Sumer, a water authority at Turkey's Selcuk University.

They are not the only ones facing international water issues. About 261 transboundary basins support 40 percent of the world's population. The United Nations says the number affected by water scarcity due to climate change is expected to more than double to 1.8 billion by 2025.

The Euphrates and Tigris, meanwhile, have the second-fastest rate of groundwater storage loss after India, according to a Chatham House report. Satellite data show many of the biggest aquifers being depleted at unsustainable rates.

Turkey, which uses about 41 percent of its water resources while Middle Eastern countries consume most of theirs, says the falling water levels are the result of others' poor downstream management, failure to make repairs and conflict.

Leaks alone cost Syria 60 percent of its water, the International Committee of the Red Cross says.

Fair Share?

Turkey's position does little to mollify the Iraqis.

"Water levels are at a record low" because Turkey is taking more than a fair share, Shorooq al-Abayachi, deputy head of the Iraqi parliament's agriculture and water committee, said.

Islamic State agrees. Water shortages are the "biggest challenge" it faces, it said in a May video. The group accused Turkey last August of reducing supplies to exert control, a charge Turkish authorities deny.

The militant group has itself targeted water facilities in Ramadi and at the Haditha dam in Iraq, part of a "disturbing new trend," the ICRC said.

"We're in danger of agriculture dying in the very region which saw it rise," said Azzam Awash, who runs an NGO helping preserve Iraq's wetlands. Those areas were drained in the 1990s by Iraq dictator Saddam Hussein to punish locals who opposed him. Only in recent years was it reflooded and seeing a revival of plants and animals.

The Arab daily Asharq Alawsat reported in June that areas of the marshlands are again being deliberately dried out, this time by Islamic State, using similar tactics as Saddam to cut off water.

"There's enough water to go around but the conflict with Islamic State has weakened" Iraq and Syria's ability to negotiate resource-sharing agreements with Turkey, Awash said.

The result may be a vicious circle where water shortages exacerbate the conflict, in turn blunting resource management.

Water "played a significant role in the instigation of the civil war in Syria," Famiglietti said. "Is it still playing a role in the continued unrest? Intuitively I think yes."