There are no major rivers in the country. Of the small rivers and streams, the only one that is navigable is the Karun, which shallow- draft boats can negotiate from Khorramshahr to Ahvaz, a distance of about 180 kilometers. Several other permanent rivers and streams also drain into the Persian Gulf, while a number of small rivers that originate in the northwestern Zagros or Alborz drain into the Caspian Sea. On the Central Plateau, numerous rivers, most of which have dry beds for the greater part of the year, form from snow melting in the mountains during the spring and flow through permanent channels, draining eventually into salt lakes that also tend to dry up during the summer months. There is a permanent salt lake, Lake Urmia (the traditional name, also cited as Lake Urmiyeh, to which it has reverted after being called Lake Rezaiyeh under Mohammad Reza Shah), in the northwest, whose brine content is too high to support fish or most other forms of aquatic life. There are also several connected salt lakes along the Iran-Afghanistan border in the province of Baluchestan va Sistan.