It is thought that the waterway formed relatively recently in geological time, with the Tigris and Euphrates originally emptying into the Persian Gulf via a channel further to the west.

[1] The Karun, a tributary which joins the waterway from the Iranian side, deposits large amounts of silt into the river; this necessitates continuous dredging to keep it navigable.

[7] The Shatt al-Arab is formed by the confluence of the Tigris and Euphrates rivers at Al-Qurnah, and flows into the Persian Gulf south of the city of Al-Faw.

Even afterwards, backtracking and disagreements continued, until British Foreign Secretary, Lord Palmerston, was moved to comment in 1851 that "the boundary line between Turkey and Persia can never be finally settled except by an arbitrary decision on the part of Great Britain and Russia".

A protocol between the Ottomans and the Persians was signed in Istanbul in 1913, which declared that the Ottoman-Persian frontier run along the thalweg, but World War I canceled all plans.

[17] The Shah argued that the 1937 treaty was unfair to Iran because almost all river borders around the world ran along the thalweg, and because most of the ships that used the Shatt al-Arab were Iranian.

[15] However, given Iran's greater military strength and population, the Iraqis decided against war, and chose to make concessions to Tehran to end the Kurdish rebellion.

[15] However, the Algiers Accord saw Iran cease supporting the peshmerga as the Iranians closed the frontier, causing the Kurdish rebellion to promptly collapse.

[21] The British journalist Patrick Brogan wrote that "the Iraqis celebrated their victory in the usual manner, by executing as many of the rebels as they could lay their hands on".

[20] When Al-Faw peninsula was captured by the Iranians in 1986, Iraq's shipping activities virtually came to a halt and had to be diverted to other Arab ports such as Kuwait and even Aqaba, Jordan.

Conflicting territorial claims and disputes over navigation rights between Iran and Iraq were among the main factors for the beginning of the Iran–Iraq War that lasted from 1980 to 1988, when the pre-1980 status quo was restored.

Since it is the only outlet to the Persian Gulf, its capture was important in delivering humanitarian aid to the rest of the country,[20] and stopping the flow of operations trying to break the naval blockade against Iraq.

[citation needed] The British Royal Marines staged an amphibious assault to capture the key oil installations and shipping docks located at Umm Qasr on the al-Faw peninsula at the onset of the conflict.

Following the end of the war, the UK was given responsibility, subsequently mandated by United Nations Security Council Resolution 1723, to patrol the waterway and the area of the Persian Gulf surrounding the river mouth.

On two separate occasions, Iranian forces operating on the Shatt al-Arab captured British Royal Navy sailors who they claim trespassed into their territory: The river is also known in Iraq as the Dijla al-Awara (دجلة العوراء) and in Iran as the Arvand Rud (Persian: اروندرود, lit.