Despite being characterized by the presence of large deserts, the Iranian territory has a complex hydrography, in which the seas surrounding the coasts and the 33 lakes scattered throughout the country have an important function, which are fundamental not only for their obvious water support, but also for their scenic beauty.
The Persian Gulf is that shallow portion (240,000 sq km) of the Indian Ocean that stretches between the Arabian Peninsula and south-eastern Iran. It is 990 km long, and its width varies between a maximum of 338 km. and a minimum of 55 km. (the Strait of Hormuz). To the north, north-east and east it laps Iran, to the north-west Iraq and Kuwait, to the west and south-west Saudi Arabia, Bahrain and Qatar, and to the south and south-east the Arab Emirates United and partly Oman. Among the numerous islands that dot it, the best known, for different reasons, are Kish, Qeshm, Abu Mussa, the Great and the Little Tonb. The main ports overlooking the Persian Gulf are Abadan, Khorramshahr, Bandar Khomeini, Bushehr, Bandar Abbas, but practically all the port cities of this coast are also of great importance for international maritime traffic.The Iranian coast is mostly mountainous , with many cliffs; in other places it is narrow and flat, with beaches and small estuaries. The flat coast widens north of Bushehr on the eastern side of the gulf and then turns into the wide plain of the delta of the Tigris, Euphrates and Karoun rivers. Its profile is very asymmetrical: along the Iranian coast the waters are deeper, while along the coast of Arabia they do not exceed 36 meters in depth-Some seasonal streams flow into the coasts of Iran south of Bushehr, but essentially none real river flows into the gulf on its southwestern bank. Large quantities of fine sand are carried to the sea by the north-east winds that blow from the inland desert areas. The deeper parts of the Persian Gulf along the Iranian coast and the area around the Tigris and Euphrates delta are mostly covered with gray-green mud rich in calcium carbonate. bad weather: high temperatures, but also strong winds which can get quite cold at the north-western ends. The rains are sporadic, mainly downpours between November and April, more intense in the north-east. Humidity is very significant; cloud cover, not abundant, is more frequent in winter than in summer. Thunderstorms and fog are rare, but sandstorms and haze often occur in the summer.Until the discovery of oil in Iran (1908), the Persian Gulf area was especially important for fishing, pearl harvesting, packaging of the sails, the cultivation of dates and other minor activities. Today, however, the crude oil industry prevails in the economy of the region.
To the north, the country borders the Caspian Sea which, although the name may be misleading, is in fact a lake, the largest in the world. It covers an area of 370,000 sq km and measures 1210 km from north to south and between 210 km and 439 km from east to west. The Caspian Sea is five times larger than the second largest of the world’s lakes (Lake Superior, on the border between the United States and Canada) and contains 44% of all lake waters in the world. It has very important tributaries such as the Volga, the Zhem and the Ural, but has no outlet to the ocean. The Caspian Sea has a salinity that is one third of that of sea water; its surface is 30 meters below sea level, but its level increases alarmingly from year to year (from 15 to 20 cm per year) .On average it has a depth of 170 m, almost double compared to that of the Persian Gulf. Its fish population is abundant; its coasts, however, offer very few natural ports, and the violent and sudden storms that characterize it make it dangerous for small boats. The main ports on the Caspian are Bandar Anzali, Nowshahr and Bandar Turkman.In addition to the Caspian Sea, the most important of the Iranian lakes is Lake Orumieh, in western Azerbaijan, 130 km long and 50 wide, and there are numerous ports overlooking the its salty waters.
There are numerous salt lakes in Iran and among these we should mention the Howz-Sultan Lake between Tehran and Qom, 20 km long and 15 km wide, which is entirely covered with salt; Lake Hamoun, in eastern Sistan, which serves as a border between Iran and Afghanistan; Lake Bakhtegan, the largest in the province of Fars. Along the border between Iran and Afghanistan there are numerous marshy lakes that widen and narrow according to the seasons of the year. The largest, the Sistan (or Hamoun-Sabari), in the north of the Sistan-Baluchistan region, is teeming with birds. The few streams that reach the arid central plateau are dispersed into brackish marshes. There are some major rivers, of which the only navigable is the Karoun (890 km.).must mention the SefidRud (765 km), the Karkheh (755 km), the Mand (685 km), the Qara-Chay (540 km.), the Atrak (535 km.), the Dez (515 km.), the Hendijan (488 km.), The Jovein (440 km.), The Jarahi (438 km.) And the ZayandehRud (405 km.). All streams are seasonal; spring floods cause enormous damage, while in summer many streams dry up completely. However, there are natural underground springs, which flow into the qanat.
Given the aridity of the climate, hydrography has a poorly developed network characterized by endorheism. Salt lakes and salt flats are the peculiarity of the endorheic depressions of Dasht-e Lut and Dasht-e Kavir, which quickly absorb the waters of the rivers that flow down from the mountains in spring.