Abstarct: Rivers are important as part of our natural and national resources. It is a public duty to present the Protection of rivers and fish for the use of future. but unfortunately, in Iran, due to the lack of proper management of surface water, and lack of legal certainty environmental problems have been encountered with environmental crises. This research investigates one of the most important environmental challenges of rivers, namely, environmental assessment. A case study on Babolroud River was one of the most important rivers in northern Iran. The environmental requirement of this river was estimated by three methods of Tenant, Q95% and habitat simulation method using River2D software for Indicator species (Luciobarbus brachycephalus in migration stage). The results showed that the Tenant method (Montana), is not able to meet the environmental requirements. Considering that in this method daily changes, seasonal or annual, as well as the habitat conditions of the species are not considered, such an estimate, regardless of the ecological conditions, can bring major damage to the environment during the short run. Also Q95% method as a hydrological method that just uses historical data does not consider the environmental requirements of the species species and despite the ability in some fish of the month in critical months, acceptable performance does not have. The habitat simulation method with River2D software provides a reasonable estimation of the monthly environmental liability, depending on the needs of the species, which validates the validity of this method globally. The living organisms of the river have different utility at different stages of their lives, so it is better to define an ecology regime for different fish.