Abstarct: In this study, the environmental effects of Al-Ghadir dam including the induced earthquakes, morphology changes of river and changes of quantity & quality of ground water in plain down of reservoir are investigated. The study show that dam construction results to increase of seismic parameter of β about 20 percent and increase of frequency of small earthquakes. Also, the focal depths of earthquakes after the dam construction are decreased and generally have a depth of lower than 15 km. The dam construction also led to reduce of sediment load of river and change of morphology of river in up and down of the reservoir. The increase of river velocity in down of dam cause of the floor and bank erosion. But reduce of river velocity before the reservoir results to formation of delta and meandering of river channel. Furthermore, dam construction stopped the recharge of Saveh aquifer and it result to drop of level and quality of underground water. The ground water level in Saveh plain from 25.9 meters in time of dam construction in 1995 changed to 53.7 meters in 2010. In fact, the rate of ground water drop in Saveh plain is about 2 meters per year and it may be result to great subsidence in near future. The decreasing of water table is different in south and north of Saveh fault.