Based on the improvement of natural science ideas about modern mechanisms of nature management, new concepts, principles, theory and methods of integrated management of water resources of transboundary rivers are presented. As part of the recognition of the equal importance of water resources in terms of the triad of ecology, the economy and society, the scientific and practical feasibility of considering the watersheds of transboundary river basins in the system of «runoff formation is determined - equal use - ecology», «nature management (environmental management ) - fair use - economy» and «society - reasonable use - society», which form the Trinity of natural, activity and management functions of river basins. The methodology for assessing the water management activity of the catchment area of the basin of transboundary rivers with integrated management of their water resources, including the author's version, which is presented in the form of four interrelated blocks : waterpotential; technical and economic potential; ecological and water management potential; socio-ecological potential.