Water is very important as one of the main factors of human life for drinking as well as purposes related to human life and human nature. Increasing demand of water caused the emerging science of dam engineering and also construction large
dams for agricultural purposes, drinking, industry and also flood control, power generation, recreational and tourist use and etc. Large dams can remarkably effect on the environment as a nonstabilizing factor in nature in various stages of construction, operation and end of life by stopping the flow of the river and stored water. However, if the environment cannot tolerate this instability, the results of the destruction of this structure will gradually rise and the objective of dam construction will be lost. The reality is that, the environmental effects are not considered fully and completely for the most dams have been constructed in Iran. In this paper, we will review the environmental impact of construction large dams on some rivers in the country and after that we will investigate some ways to deal with the effects and finally we will separately examine the use of several small dams instead of big dams as an important and effective option.