The environmental feasibility assessment of the construction and operation of nuclear power stations in near-border areas must take into account the requirements of the international and European environmental legislation. For the study on environment feasibility assessment of the Baltic NPP to meet the international standards, the following steps were taken: the content and the application practice of UNECE Convention on Environmental Impact Assessment in a Transboundary Context (Espoo) to NPP substantiation were analyzed and compared with the Russian procedure of environmental impact assessment (EIA); water quality standards for water bodies used for fishery and the approaches to assessing the damage to aquatic bioresources in Russia, Lithuania (EU), and Belarus were compared. A transboundary network for monitoring aquatic ecosystems was developed in the zone of potential influence of the Baltic NPP, and a permanent mathematical model was developed and used to forecast the effect of the anticipated water discharge from the station on the hydrodynamic, chemical, and temperature regime of the Neman R., whose results were used to forecast the impact of water intake and discharge facilities of the Baltic NPP on the food base and migration character of ichthyofauna.