large saline lake in southwestern Tunisia, occupying a salt-flat basin of about 1,900 square miles (4,900 square km). The lake is covered with water only in the lowest areas, except after periods of heavy rains. Together with Chott El-Fedjaj (Shaṭṭ Al-Fijāj) and Chott Al-Rharsa (Shaṭṭ Al-Gharsah) in Tunisia and Chotts Melrhir (Melrhir, Chott) and Merouane in Algeria, the lake forms a depression that was formerly an arm of the sea and that extends nearly 250 miles (400 km) westward from the Gulf of Gabes. This depression's floor reaches 52 feet (16 metres) and 69 feet (21 metres) below sea level in Jarid and Rharsa lakes, respectively. The extensive salt flats of Chott El-Jarid have been an important source of phosphates since the discovery of the mineral there in 1949. The flats are now crossed by a roadway that has become a route for tourists visiting the desert oases and hinterland towns. Tozeur (Tawzar) and Nefta (Nafṭah), the main oases towns on the lake's periphery, are noted for their date palm production.