Twelver Shi'i Islam is totally dominating the Iranian society, not only as creed, but also with its impact on the political system.
There is a vastly extended network of rivers in Iran most of which seasonally are filled with water. Some permanent rivers run from the Alborz or the Zagros to the Caspian Sea, Persian Gulf and Oman Sea.
Twelver Shi'i Islam is totally dominating the Iranian society, not only as creed, but also with its impact on the political system.