Gotvand-Olia as one of the largest constructional projects in Iran has been constructed on the Karoun River, between Masjed Soleiman and Gotvand Regulatory dam in Khuzestan Province. It is situated in 382.8 km away from the river estuary at a distance of 25 km north of Shoushtar city. This study was conducted to identify and assess the risk of Gotvand-Olia dam on the environment at the operational phase. As a part of the management of water resources, the dam is one of the most important structures playing a major role in the regulation of surface flows, especially in the areas that have poor spatial and temporal distribution of rainfalls. Due to developments in dam construction in the world and particularly in Iran, the need to assess the environmental impacts of dams is very important. Environmental risk assessment is able to establish a relationship between the impacts of unwanted events with those that are not catastrophic. The quantitative risk assessment provides evident objectivity and transparency in the assessment of the impacts.