Shatt Al Arab

Shatt Al Arab, river in south-west Asia, serving as a boundary between Iraq and Iran, and formed from the merging of the Euphrates and Tigris rivers in Iraq as they approach the sea. The waterway is roughly 170 km (110 mi) long, and runs from the confluence of the Euphrates and Tigris to the head of the Persian Gulf near Kuwait. Its major tributary below the confluence is the Kārūn river, which flows from Iran. The area surrounding the Shatt Al Arab is largely alluvial lands and swamps. This marshy landscape is the habitat of an Arab people who, through their relative isolation, have developed a distinctive culture reliant on the marsh environment.

Sediment from the river's tributaries is deposited at the mouth in the Persian Gulf, continually extending the delta area; as a result, the Iranian city of Ābādān, which 1,000 years ago was on the shore of the Gulf, is today 50 km (31 mi) inland. Because of the large silt content, the river must be frequently dredged to remain navigable. Oil is produced, stored, and shipped from this area, and the banks of the Shatt support the world's greatest concentration of date production. Ābādān, the Iraqi city of Basra, and the port of Khorramshahr in Iran are the major commercial and population centres on the river.

The Shatt Al Arab is a vital strategic waterway, as it constitutes Iraq's only access to the seas and provides a transport corridor for oil exports and commodity imports for both Iran and Iraq. Control of the river has long been contested, and was the ostensible cause of the decade-long Iran-Iraq War that began in 1980. The earliest documented dispute over the waterway goes back to the Treaty of Zohab in 1639. This treaty was intended to establish a boundary between the Persian and Ottoman empires. The language of the treaty was vague, however, and conflict over the Shatt persisted through a number of subsequent agreements.

Outside powers got involved in the issue during the 19th century, with Russia backing Persian claims to the eastern bank of the river, and Britain supporting Ottoman claims to control of both banks. The Second Treaty of Ezerum, signed in 1847, generally confirmed the Russo-Persian position, but the language was such that the Ottomans claimed ownership of the entire Shatt Al Arab, while ceding navigation rights to the Persians. Agreements signed just prior to World War I shifted the boundary to the middle point of the channel opposite a number of ports on the Persian side of the river, but generally the boundary between the two powers remained on the eastern bank of the waterway.

Disputes along the river, ranging from encroachment to blockades, have accompanied a regular process of treaty negotiation and abrogation over the years, and have continued after the dissolution of the Persian and Ottoman Empires, with the contention being taken up by their successor states in the region, Iran and Iraq respectively. The increase in regional oil production in the 1960s and 1970s served to intensify the conflict. With the outbreak of the Iran-Iraq War in 1980 the Shatt Al Arab became a battlefield, and both sides were forced to divert oil to other ports for loading. Since the conclusion of that war the waterway has largely been rehabilitated.