Karun River is the largest and most watery river in Iran. At first, the water current flowed straight to the sea. But later the locals built this dam to irrigate their crops. It is divided into two branches of Gargar and Shatit at the entrance to Shushtar. Mizan dam of Shushtar is a dam which is built to divide the water flow of the river into 2 and 4 proportions between Gargar and Shatit rivers. So, the Gargar River is called Dodangeh (2 proportions) or Mosraqan; and the Shatit River is called Chardangeh (4 proportions).
This dam is attributed to the Shapur First of the Sassanid Dynasty. It was built using the materials such as stone (carved stones of Shushtar) and mortar. The Mizan dam along with other Historical Hydraulic Structures of Shushtar has caused the irrigation 40 thousand hectares of Mianab plain in Shushtar. Therefore, Salasel Castle