Shatt al Arab

Shatt al Arab, river in southwest Asia, serving, for about the second half of its course, as a boundary between Iraq and Iran. The waterway is 170 km (110 mi) long, and flows from the confluence of the Euphrates and Tigris rivers in Iraq to the head of the Persian Gulf near Kuwait. The Kārūn River, which originates in Iran, is its major tributary. The area surrounding the Shatt al Arab consists largely of alluvial lands and swamps. Sediment from the river’s tributaries is deposited at its mouth in the Persian Gulf. Over time, these deposits have extended the Shatt al Arab delta and caused the gulf to recede. As a result, the Iranian city of Ābādān, though on the Persian Gulf 1,000 years ago, now lies 50 km (30 mi) inland, on an island in the Shatt al Arab.

Besides Ābādān, major ports on the river include Al Başrah in Iraq and Khorramshahr in Iran. The Shatt al Arab is a vital strategic waterway, as it constitutes Iraq’s only access to the sea and provides a transportation corridor for oil exports and commodity imports for both Iran and Iraq. Due to its economic and strategic significance, control of the river has long been contested. The earliest documented dispute dates to the Treaty of Zohab of 1639. This treaty was intended to establish a boundary—partly at the river—between Persia (now Iran) and the Ottoman Empire (including what is now Iraq). The language of the treaty was vague, however, and conflict over the Shatt al Arab persisted through a number of subsequent agreements. Outside powers became 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 Erzurum, signed in 1847, generally confirmed the Russo-Persian position, but again the language was so vague that the Ottomans claimed ownership of the entire Shatt al Arab, while ceding navigation rights to the Persians. Under agreements signed just prior to World War I (1914-1918) the boundary remained on the river’s eastern bank except around Khorramshahr and Ābādān, where it shifted to the middle point of the river. Disputes since that time, ranging from encroachment to blockades, have accompanied a regular process of treaty negotiation and annulment. The increase in regional oil production in the 1960s and 1970s served to intensify the conflict, and control of the Shatt al Arab was one of the causes of the Iran-Iraq War (1980-1988). The river became a battlefield, and both sides were forced to divert oil to other ports for loading.