a case study in Rayong and Pathum Thani Provinces Jaffel, Khouloud creator Thammarat Koottatep Chairperson Gunasekara, Kavinda Examination committee Tatchai Pussayanavin Examination committee Thamasak Yeemin Examination committee Government of Japan Scholarship Donor text series technical report th Pathum Thani, Thailand Asian Institute of Technology 2022 continuing eng 45 leaves : ill. Ocean plastic pollution comes from two main sources, including both land- and sea-based activities, and is often related to the mismanagement of municipal, industrial, and agricultural solid waste, as well as lost or abandoned fishing gear (LAFG). While acknowledging that smaller plastic particles (including microplastics) are of high interest and concern, this study investigates the ingestion of microplastics by freshwater and marine fish in Pathum Thani and Rayong provinces. It also includes data mapping to illustrate how plastic pollution correlates with a number of factors, including population density, marine protected areas, marine water quality index, leakage rate, and plastic waste management, identifying these factors would influence decision-making in tackling marine litter. To this end, this study aims to investigate the abundance (color, size, shape) of MPs ingested by freshwater and marine fish from Thailand. A total of 3 freshwater fish and 10 marine fish were studied. The results revealed that all fishes had ingested plastic debris. The predominant color in both marine and freshwater fish was blue (50%) and (52%), respectively, followed by transparent and red color. The occurrence of fibers in marine fish (92%) was larger than in freshwater fish (49%), probably due to fishing activities in the study area. Microplastics less than 5 millimeters in size were most abundant in freshwater fish (98%) compared to marine fish (85%), while mesoplastics (5-25 mm) were most abundant in marine fish (15%) compared to freshwater fish (2%). In addition, the results of GIS mapping showed that all areas with the highest population density and poor water quality index are located near the coastline or crossed by rivers, which favors plastic waste leakage. It also shows high intensity of human activities, open dumpsites and resource use in Marine Protected Areas (MPAs). A research study submitted in partial fulfillment of the requirements for the degree of Master in Marine Plastics Abatement Research studies project report (M.) - Asian Institute of Technology, 2022 Microplastics Environmental aspects Thailand Asian Institute of Technology. http://203.159.5.9/ait-thesis/detail.php?q=B17479 http://203.159.5.9/ait-thesis/detail.php?q=B17479 221005 20260818134211.0