The Sinos River is the main water body of the Sinos River Basin. Located in the state of Rio Grande do Sul, Brazil, it comprises 32 municipalities and supplies water for more than 1.6 million inhabitants. Human activities are vastly diversified along the watershed, directly reflecting on its environmental quality once it recieves constant domestic and industrial untreated wastewater discharges. Given hydrological and geomorphological characteristics, the basin is subdivided into three sections: upper, middle, and lower. The first section refers to a region closer to the source of the Sinos River, with low anthropogenic influence and mainly rural land-use. The second section has a transition aspect and presents both rural and urban features. Finally, the lower section, has the highest level of anthropic pressure, is densely populated and highly industrialized. To date, studies evaluating the presence of microplastics in this important freshwater ecosystem are scarce. In this sense, aiming to assess the occurrence of microplastics in the Sinos River, surface water and sediment samples were collected at sites in Caraá (upper), Parobé (middle), and São Leopoldo (lower) sections along the riverbank. Samples were preserved in controlled conditions. After laboratory procedures, samples were vacuum-filtrated using cellulose acetate membrane filters. A quali-quantitative analysis was performed and according to specific literature, the filters were observed under a stereomicroscope and the particles were counted and classified. Precautions were taken in all steps to avoid external contamination. It was possible to observe several microplastics in all samples from the three sites analyzed. In general, fibres were the predominant shape found. These findings are part of a larger ongoing research developed at Feevale University and the final results will lead to important contributions regarding microplastic pollution at state and regional levels.