A development project is analysed from three major components- Impact on Environmental Health, Economic Profitability, and Socio-Economic Equity to measure its Sustainability. The preliminary study was conducted through Interviews with the NHPC authorities entrusted with the responsibility of construction and management of the dam and the local people residing within the vicinity of the project area. The NHPC authority clarified from their end that the dam construction will bring sustainability from the economic end by generating 2000 MW of electricity which can enrich the country as a whole and the state of Assam and Arunachal Pradesh in particular by increasing the Hydroelectric power generating potential of the country and thereby removing the scarcity of power in both the states. Clearance of the National Green Tribunal also nullifies the issues of the local organizations mostly from the downstream area of the dam i.e. Assam regarding the impact of the dam on local ecology and livelihood of the riparian people residing in the downstream area. At the Socio-economic level, under its CSR project, NHPC authorities have conducted many awareness programs and even developed an e-website to promote women weavers for its brand SAAR Subansiri Handloom. Contrasting views were expressed by the people of downstream and upstream areas regarding the impact of the dam. While the upstream people are satisfied with the construction of dams since they are receiving free electricity, monetary compensation, and permanent jobs in the project the downstream people are denying any kind of benefit either from the government or from the NHPC authority. Moreover, the high voltage electric wires that cross over the nearby residential areas of the dam and the discharged dam water during the rainy and flood seasons pose a threat to the lives of the people and domestic cattle. In the case of employment also the downstream are employed only as casual labourers. The downstream people are also denied of compensation as per the dam displacement law – people residing within the 5 km vicinity of the project if anybody is displaced should receive compensation. So, the question of the sustainability of the LSHEP remains unresolved creating protests against the dam