River of the Middle East, 1959 kms long, rising in Turkey – in the predominantly Kurdish area – and flowing into the Arab-Persian Gulf after having formed for over one hundred kilometers the border between Syria and Turkey and crossed Iraq where it forms, with the Euphrates, the Shatt-El-Arab 200 kilometers before joining the sea. Its annual average flow in Iraq is 53 billion m³ but, like the Euphrates, this flow is very irregular: over half of its total annual flow takes place in the space of three months (March, April and May). It is the largest of the two Mesopotamian rivers whose combined flow is nearly equivalent to that of the Nile.

Unlike the Euphrates, most of the water (between 48 and 55%) of the Tigris originate in the Iraqi mountains, the other part coming from Turkey (no Syrian water drains into the Tigris).

Turkey and Syria both have projects to use part of the Tigris which are more than likely to cause future problems for Iraq but not to such an extent as the Turkish « GAP » (Great Anatolia Project) on the Euphrates in the near future.