This article talks of the various governance lessons that the Mekong basin bears for the Ganges–Brahmaputra–Meghna (GBM) basin. It highlights the existing hydropolitical and ecological problems associated with the GBM basin, the reasons for which are attributed to the reductionist colonial engineering paradigm also delineated in this article as ‘arithmetic hydrology’. The transboundary interactions in the GBM to resolve the problems have largely relied on an issue-based, piecemeal, fragmented approach that has further complicated the problems. It is in this context, the article brings in how a cooperative mechanism in the institutional form of the Mekong River Commission (MRC) has been attempting to promote a participative and integrated approach to river basin governance. The article, therefore, talks of some of the replicable practices and learnings that may help in takeaways for the GBM riparians and stakeholders from the Mekong system. JEL Codes: F02, N50, Q01, Q22, Q24, Q25, Q28