Healthy river ecosystems are essential for sustaining the natural environment and human society. Understanding of the material fluxes in river basins, including those related to water, sediment, nutrients, natural organic matter, trace materials, emerging contaminants, living organisms, and greenhouse gases, could enable to improve monitoring and restoration of river ecosystems. An overview of the current status of approaches and results necessary for accounting for all material fluxes (AMF) in large rivers is thus of the utmost importance. The 3^rd International Conference on All Material Fluxes in River Ecosystems (AMFR 2026) will provide a global forum for a wide-ranging discussion of key issues related to research on various material fluxes, their interactions, ecological responses, and sustainable management in aquatic ecosystems. A primary aim of this conference is to promote future collaboration between the participants on research into AMF in multi-sphere systems.