Shatt al-Arab

The Arvand River or Shatt al-Arab is a river of some 200 kilometres in length that is formed at the confluence of the Euphrates and Tigris rivers in the town of al-Qurnah in the Basra Governorate of southern Iraq. The southern end of the river constitutes the Iran–Iraq border down to its mouth, where it discharges into the Persian Gulf. The Shatt al-Arab varies in width from about 232 metres at Basra to 800 metres at its mouth.

Source: Wikipedia