Agricultural Water development projects modify the downstream flow regime resulting in changes in riverine biodiversity. This study attempted to predict the likely impacts of flow regulation on riparian plant composition.The study was conducted in the upper part of Blue Nile basin in the northwestern part of Ethiopia. Floristic composition was studied to assess the presence of plant species that could be affected by the storage and regulation of the River water. Flow history was also examined to analyze the likelihood of disturbance in scenarios with and without flow regulation. The vegetation analysis indicates that the majority of the downstream vegetation prefers moisture rich substratum. On the other hand, the hydrological analysis shows that the dam may lead to reductions in maximum daily discharges. Therefore, Reductions in flood peaks and over-bank flows could result in changes in species composition and diversity of plants growing in water rich substratum below the dam. The information from this study is important and it is hoped it will be used by ecosystem modelers and conservationists concerned with environmental risk assessment; environmental protection and monitoring.