Persian Gulf flooding of the basin started 15,000 years ago due to rising sea levels of the Holocene glacial retreat. This inland sea of some is connected to the Gulf of Oman in the east by the Strait of Hormuz; and its western end is marked by the major river delta of the Shatt al-Arab, which carries the waters of the Euphrates and the Tigris. In Iran this is called "Arvand Rood", where "Rood" means "river". Its length is , with Iran covering most of the northern coast and Saudi Arabia most of the southern coast. The Persian Gulf is about wide
Persian Gulf naming dispute as the Arabian Gulf". Since about 2009, due to increased cooperation with Arab states of the Persian Gulf, various branches of the United States armed forces have issued directives to their members to use the "Arabian Gulf" when operating in the area to follow local conventions ("Persian Gulf" is still used in official publications and websites). The practice of the United States Fifth Fleet, based in Bahrain, is to use "Arabian Gulf": The National Geographic Society uses the name Persian Gulf to refer to this body of water. In 2004, the society published a new edition of its "National Geographic