The Shatt al-Arab () is a river about 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 at Basra to at its mouth. 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. Kuwait's Bubiyan Island is part of the Shatt al-Arab delta.
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.
The area used to hold the largest date palm forest in the world. In the mid-1970s, the region included 17–18 million date palms: an estimated one-fifth of the world's 90 million palm trees. However, by 2002, more than 14 million of the palms had been wiped out by the combined factors of war, salt and pests; this count includes around 9 million palms in Iraq and 5 million in Iran. Many of the remaining 3–4 million trees are in poor health.
Naming
The river is also known in Iraq as the Dijla al-Awara (دجلة العوراء) and in Iran as the Arvand Rud (, ).
The Persian epic poem Shahnameh (written between ) and many other works of Middle Persian literature use the name Arvand () for the Tigris River, the confluent of the Shatt al-Arab. Iranians also used this name specifically to designate the Shatt al-Arab during the later Pahlavi period, and continue to do so since the 1979 Iranian Revolution.
History
The Shatt al-Arab originally extended to the Ur Schatt river system that fed the Pleistocene/Holocene Arabian Gulf Oasis, a system of linked lakes and flood plains that stretched to the Strait of Hormuz and emptied into the Gulf of Oman. This system flooded in the period 12,000 - 7,000 BCE to form the present-day Persian Gulf.
Dispute over the river occurred during the Ottoman-Safavid era, prior to the establishment of an independent Iraq in the 20th century. In the early 16th century, the Iranian Safavids gained most of what is present-day Iraq, including Shatt al-Arab. They later lost these territories to the expanding Ottomans following the Peace of Amasya (1555).
In the early 17th century, the Safavids under king (shah) Abbas I (r. 1588–1629) once again regained Shatt al-Arab. Control of the river was at last permanently ceded to the Ottomans with the Treaty of Zuhab in 1639. Control of the waterway was also temporarily lost by the Safavids to the Ottomans in this treaty. In general, the Treaty of Zuhab roughly re-established the common borders of the Ottomans and Safavid Empires the way they had been in 1555. However, the treaty never demarcated a precise and fixed boundary regarding the frontier in the south.
Later, Nader Shah (r. 1736–1747) succeeded in restoring Iranian control over Shatt al-Arab for a time. With the Treaty of Kerden (1746), however, the Zuhab boundaries were restored, ceding the river to the Turks once again. The First Treaty of Erzurum (1823) concluded between Ottoman Turkey and Qajar Iran, resulted in the same.
The Second Treaty of Erzurum was signed by Ottoman Turkey and Qajar Iran in 1847 after protracted negotiations, which included British and Russian delegates. 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.
thumb|left|Coat of arms of the Kingdom of Iraq 1932–1959 depicting the Shatt and the forest
During the Mandate of Iraq (1920–1932), the British advisors in Iraq were able to keep the waterway binational under the thalweg principle that worked in Europe: the dividing line was a line drawn between the deepest points along the stream bed. In 1937, Iran and Iraq signed a treaty that settled the dispute over control of the Shatt al-Arab. The 1937 treaty recognized the Iranian-Iraqi border as along the low-water mark on the eastern side of the Shatt al-Arab except at Abadan and Khorramshahr where the frontier ran along the thalweg (the deep water line) which gave Iraq control of almost the entire waterway; provided that all ships using the Shatt al-Arab fly the Iraqi flag and have an Iraqi pilot, and required Iran to pay tolls to Iraq whenever its ships used the Shatt al-Arab. Shah Reza Shah of Iran together with his close friend President Mustafa Kemal Atatürk of Turkey had been promoting the Saadabad pact intended to protect the neutrality of Muslim nations if the world should be plunged into war again. In return for the Shatt al-Arab treaty, Iraq joined the Saadabad pact and Iranian-Iraqi relations were friendly for decades afterward.
The Shatt al-Arab and the forest were depicted in the middle of the coat of arms of the Kingdom of Iraq, from 1932 to 1959.
thumb|upright|Arab ferryman on the Shatt al-Arab 1958
thumb|Evening atmosphere on the Shatt al-Arab
Under Shah Mohammad Reza Pahlavi in the late 1960s, Iran developed a strong military and took a more assertive stance in the Near East. 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. Iraq threatened war over the Iranian move, but on 24 April 1969, an Iranian tanker escorted by Iranian warships (Joint Operation Arvand) sailed down the Shatt al-Arab, and Iraq—being the militarily weaker state—did nothing. In the winter of 1974–75, Iran and Iraq almost went to war over Iran's support of the Kurds in Iraq (see 1974–75 Shatt al-Arab conflict). The Algiers Accord was seen as a national humiliation in Iraq, causing much bitterness over what was seen as Iranian bullying. 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". After retaking Al-Faw, the Iraqis began a sustained drive to clear the Iranians out of all of southern Iraq. In May 1988, the Iraqis expelled the Iranians from Salamchech and took Majnun Island. Brogan reported: