Introduction . Plastic pollution is increasing in many aquatic systems1 , 2and is already a global concern3. Plastics in water can negatively impact human livelihoods and aquatic organisms and be a potential risk to human health4 , 5 , 6 , 7. Approximately 0.8–23 million tons of plastics enter seas worldwide annually8 , 9 , 10 , 11 , 12. Rivers may contain both macro- (>5?mm)13and microplastics (<5?mm)14, but their sources are not well-...