<p>River watersheds, particularly those spanning multiple countries, pose significant environmental, legal, and political challenges in managing water resources sustainably. This qualitative study examined the controversial conservation and restoration of river watersheds under international legal responsibility with a case study of the Mekong River. It employed a case study through a comparative policy analysis approach to exploit the secondary sources, especially targeting the Mekong River Basin. The study analyzed the legal obligations of the riparian countries - Vietnam, Cambodia, Laos, Thailand, and China - under international law, alongside their respective water management policies. The data were gathered through a comprehensive review of primary and secondary sources, including legal documents, international treaties, academic literature, and case law. The results highlighted significant disparities in the implementation of water conservation policies, with some countries prioritizing economic growth over ecological sustainability. Furthermore, it uncovered the intricate interplay among international law, environmental ethics, and the political dynamics involved in the management of transboundary rivers. The findings indicate that despite the existence of international legal frameworks, they require substantial reforms to balance economic development with environmental conservation more effectively. Besides, more enhanced cooperation among the riparian countries and stronger enforcement mechanisms are essential to achieving long-term ecological sustainability and equitable growth for the Mekong River ecosystem.</p><p> <?noindent??><b>Clinical trial number</b>: Not applicable.</p>