Plastic pollution is an emerging global concern, yet semi-urban and remote riverine systems remain critically understudied. These environments play a vital role in linking human activity to transboundary ecosystems, but pathways of anthropogenic pollutants are poorly understood. This project aims to investigate the actionable evidence on the sources, pathways and dispersal of macroplastics in two rivers: Houxi River in China and Kherlen river in Mongolia. Through scientific methods with community-driven monitoring, the project will characterise pollutant behaviour and deliver knowledge for future solutions and mitigation. We will conduct systematic field sampling, laboratory analysis, spatial mapping of macroplastics, modelling and citizen science initiatives where locals contribute for waste collection. This approach benefits both scientists and locals by strengthening scientific data through expanded field sampling and empowering communities by offering direct engagement on pollution issues. This study will provide a holistic assessment of macroplastics by examining their origins, behaviours and transport pathways. From a socio-ecological perspective, the project will establish community-based monitoring programs and deliver findings in local languages to ensure accessibility and relevance. By co-developing mitigation strategies with stakeholders, the project strengthens environmental resilience and fosters public awareness of pollution in semi-urban riverine ecosystems.