The Nemencha mountains—eastern extensions of the Atlas chain—divide the country into two distinct regions, the well-watered north and the semiarid south. The latter includes Tunisia's highest point, Jebel Chambi, 1,544 m (5,064 ft), near Kasserine. The northern region is further divided into three subregions: the northwest, with extensive cork forests; the north-central, with its fertile grasslands; and the northeast, from Tunis to Cape el-Tib, noted for its livestock, citrus fruits, and garden produce. The southern region contains a central plateau and a desert area in the extreme south, which merges into the Sahara and is characterized by date palm oases and saline lakes, the largest of which is Chott el Djerid. The Medjerda, the most important river system, rises in Algeria and drains into the Gulf of Tunis.