The area of the Caspian Sea is about 422,000 km2 with 6397 km coastline, of which more than 900 km is along the Iranian side. About 128 large and small rivers flow into the Caspian Sea from Iran, among them the four largest rivers are: Sepidrud, Shalman, Shafarood, and Toneká bon. The highest salinity level reaches 12.7 ppt (about 1/3 of the ocean salinity) during summers. The average water temperature in the coastal regions throughout the year ranges from 15.9oC to 17oC. Temperature difference between the coldest area in the north, and the warmest area in the south is 4oC during winter and 16oC during summer.
