The correct answer is - the dams Turkey is building on the Euphrates River.
Syria is a country dominated by arid and semi arid climate. It lacks on water resources, and the only big river that is providing water for irrigation is the Euphrates River.
On the other hand, Euphrates runs through Turkey first before it enters the territory of Syria, and since it runs through the driest part of Turkey, the Turkish government decided to build numerous dams on Euphrates. The purpose of the dams is to enable enough water for irrigation and to develop the agriculture in the eastern part of the country.
Unfortunately for Syria, the numerous dams in Turkey means much less water is coming through Euphrates in their territory, and that is directly damaging the agricultural production as it creates a lack of water.
