Water pollution caused by microplastics generated from land-based sources (e.g. as tire-wear particles, broken road markings, synthetic textile microfibre from washing, microbeads from personal care products, discharged domestic wastewater from households, and others) is attracting attention in many countries and regions around the world as an emerging environmental problem, not only at national and regional level, but also worldwide. Microplastics released from these sources often flow directly or indirectly into surrounding aquatic environments such as rivers and lakes, and eventually enter the ocean. The adverse impacts of microplastics on ecosystems and aquaculture organisms have been well-reported, and they may gradually cause potential adverse effects on human health as well. Unfortunately, in most member states in the Association of Southeast Asian Nations (ASEAN), basic knowledge about the occurrence, ingestion and impacts of riverine microplastics pollution on ecosystem and human health is very limited. As a result, appropriate and effective countermeasures to control the emission of microplastics have not yet been established. This Discussion Paper presents a concise and insightful review of the current state of knowledge on the occurrence, ingestion and impacts of microplastics on ecosystems and human health. Moreover, due to the transboundary nature of plastic litter issues, any solutions implemented in single country will not be sufficient to address these regional and transboundary issues. The paper calls for collective efforts from all the ASEAN Member States to address issues along the plastic value chain through the circular economy approach, from raw material extraction, design, production, distribution, responsible plastic consumption (especially single use plastic products), collection/reuse/repair, to the recycling stage and final disposal.