Today, large amounts of water pollutants, including pharmaceutical waste, paints, plastics, pesticides and mineral waste, are discharged by humans into the nature. One of the emerging pollutants that seriously affects water quality is microplastics. The growing global concern about human exposure to microplastics necessitates research on their abundance, fate and effects. This study was conducted with the aim of investigating the spatial distribution of microplastics and determining their possible source from the source to the tributary of the Zayandeh Rood River. For this purpose, water sampling was done from 17 stations and the samples were taken to the laboratory. In order to digest organic matter, the samples were digested for 48 hours using 30% hydrogen peroxide and then passed through 45 micrometer filter paper. The microplastics of each filter paper were separated and counted using an optical microscope, and their type of polymer was identified by Raman. The abundance range of microplastic particles was 2-49 particles per liter and fiber and small particles were reported as the most abundant forms. The size of microplastics was reported between 50-5000 micrometers. Three polymers polypropylene, polyamide and polyethylene were also detected by Raman device. Discharge of industrial wastewater and domestic sewage, garbage disposal by tourists are the most important sources of microplastics in the region. Inventing methods to increase the efficiency of removing microplastics in sewage treatment plants and its complete removal in the final effluent is recommended as an effective solution to reduce this pollutant.