Sustainable management of rivers is essential to maintaining livelihoods, health, biodiversity, economic and food security, and more in the Western Indian Ocean region and beyond. The new Guidelines for the Assessment of Environmental Flows in the Western Indian Ocean Region aim to create a standardized, region-wide approach to conducting environmental flow assessments in rivers with a step-by-step guide to enable learning across the region. The Guidelines, the creation of which was requested by Nairobi Convention states, were developed by the UNEP–Nairobi Convention, the Western Indian Ocean Marine Science Association and the Sokoine University of Agriculture. They will be used by governments, researchers, civil society, and communities managing water resources.