This study identifies the impacts of plastic pollution on land and freshwater migratory species protected by the Convention on the Conservation of Migratory Species of Wild Animals (CMS). The CMS report is the result of a collaboration between CMS and the UN Environment Programme as part of the Japan-funded CounterMEASURE II project to identify sources and pathways of plastic pollution in river systems in Asia. Plastic pollution is a global issue with plastic waste flowing into oceans from rivers. However, it is a particular problem in the Asia-Pacific region. Two case studies in the report focus on the species of the Mekong and the Ganges, which sit among the most polluted rivers globally. The report recommends increasing research efforts to understand the negative effects on organisms and ecosystems because of plastic pollution. It calls for more effective waste management, recycling, and design of products, preventing plastic pollution at the source.