Iraq's relief can be divided into four physiographic regions: the alluvial plains of the central and southeastern parts of the country; Al-Jazirah, an upland region in the north between the Tigris and Euphrates rivers; deserts in the west and south; and the highlands in the northeast. Each of these regions extends into neighbouring countries, although the alluvial plains lie largely within Iraq. Alluvial plains The alluvial plains of lower Mesopotamia extend southward some 375 miles from Balad on the Tigris and Ar-Ramadi on the Euphrates to the Arabic Gulf. They cover more than 51,000 square miles, almost a third of the country, and are characterized by low elevation, below 300 feet (100 metres), and poor natural drainage. Large areas are subject to widespread seasonal flooding, and there are extensive marshlands, some of which dry up in the summer to become salty wastelands. Near Al-Qurnah, where the Tigris and Euphrates converge to form the Shatt al-'Arab, there are inhabited marshes. The alluvial plains contain extensive lakes. The swampy Lake Al-Hammar (Hawr al-Hammar) extends 70 miles from Basra (Al-Basrah) to Suq ash-Shuyukh; its width varies from 8 to 15 miles. Lake As-Saniyah lies west of the Tigris and extends some 75 miles southward from 'Ali al-Gharbi.