Due to increasing demand for various human needs and climate change issues, rivers are now under enormous pressure. With increasing pressure on these valuable natural resources, responses among state and non-state actors are insufficient in the Anthropocene. To fill the gap, International Environmental Law (IEL) provides several principles for better management of these resources. Equitable utilisation and minimisation of environmental harm are among the most important principles of the IEL. From a theoretical perspective, these principles should lead to the sustainability of these resources and promote cooperation among relevant actors. However, many river basins are still not allocated equitably and suffer from environmental damage. By using comparative, doctrinal, and empirical research methods, this thesis evaluates the two principles at the international level in Tigris and Euphrates River Basin, the federal level in Murray Darling Basin and at the local level in the Waikato River catchment. The research discovered major challenges for implementing the two principles. One major challenge is sovereignty, another is a lack or weakness of local voices and transparency. As the nature and status of all basins are different, the challenges are not exactly the same. For example, hearing local voices and better information transparency have significantly improved in the Waikato River. As the challenges for implementing the two principles are not purely legal, the responses should blend legal solutions with political and socio-economic solutions. Therefore, this thesis strongly supports shared sovereignty among states at the international level as well as shared sovereignty with indigenous and minority groups at the national level. Cooperation among national and international actors in the river basins is also crucial for implementing the two principles effectively. Finally, there is the opportunity to establish basin institutions or organisations to manage river basins integrated and sustainable. This is vital in the case of TE-RB because the basin still lacks an institution. Furthermore, the basin institution in the MDB requires more robust compliance and monitoring power because the provisions of the Water Act 2007 and the basin plan still have not been implemented effectively. Finally, the thesis concludes with two common lessons in comparing these cases. The first lesson is that equitable utilisation cannot be implemented effectively if it is not accepted by the local community in a broad and deep meaning. It means that the equitable allocation should be extended from only the riparian states to equitable allocation among the people within each state. The second lesson is that the minimisation of environmental harm cannot be implemented without determining the minimum flow of rivers, particularly transboundary rivers. Determining an environmental impact assessment for water projects and taking advantage of available solutions of nature contributes significantly in implementing the two principles and sustainable management of our rivers.