Iran is an arid country with an average annual precipitation of about 250 mm; less than one-third of the world average. With population growth and also development of urbanisation and economical units, the increasing water demand has caused an alarming decrease in per capita renewable water available in Iran. In addition, Iran has been experiencing severe drought conditions in recent years. In response to the need for water supply, much effort has been expended in the development and exploitation of water resources. Considering that keeping and storage of water supplies have both noticeable positive and negative impacts on the environment, enough attention has not yet been paid to the environmental impacts of dam constructions and interbasin water transfer (IBWT) project. In such situation, quality of environmental impact assessment studies can play an important role to prevent or control the predicted ecological and socioeconomic impacts. In this ongoing study, a systematic review process examined 86 impact statements related to dam construction and water transferring projects verified by DOE. This review is based on a checklist which itself draws on many sources such as USA and EU Environmental Impact Statement Checklists, recommendations of organizations and countries, studying some sample reports, and finaly through a comprehensive look on dams impact assessment. This review is to score each statement from 1 to 4. This approach provides a precise framework for judging the worth of EISs as decision making tools. Results show that the maximum quality belongs to the description of the proposed action and alternatives and minimum quality is related to predicting the effects of the project on the biological parameters. The average quality of EISs was equal to 2.3 which 44 reports had lower quality than it, the quality of 36 other reports were higher, and in 6 EISs the quality was equal to average. The overall proportion of satisfactory EIA reports sampled between 1380-1390 showed no significant change in the quality of EISs. The results revealed a number of technical and methodological weaknesses in a significant percentage of cases so this can be perceived that environmental permission and economic project benefits are considered to be more important to plan executives in comparison to environmental and its conservation. This study identifies the factors influencing the quality of EIS and makes recommendations for further improvement of the EISs quality.