Estuaries are transition zones between rivers and the ocean, which play a crucial role in the emission of plastic debris between the riverine and marine environments. These mixed ecosystems, where freshwater meets saltwater, are critical points for the accumulation and transport of microplastics (MP) (small plastic particles less than 5 millimeters in size). It has been identified that the ingestion of MP by numerous aquatic species results in their retention in the body and digestive tract, generating negative impacts on their quality of life. In this study, in order to determine the extent of contamination caused by MP, two migratory species of freshwater snails, Neritina virginea and Neritina punctulata, will be used as natural accumulators to provide information on plastic pollution in estuaries of the Río Mameyes and Río Espíritu Santo in Puerto Rico. The main objective of this study is to describe, quantify and identify the types of microplastics present in the soft body of freshwater gastropods of the genus Neritina. We hypothesize that the presence of microplastics in the soft body of Neritina virginea and Neritina punctulata will be determined by the increase of plastic pollution in estuaries and by the ability of these organisms to retain and ingest particles suspended on the bottom of the water during their exposure and scrape feeding. In this study, snail tissue samples were digested with 30% hydrogen peroxide. The MP particles were identified, counted and characterized (shape, size and color) by visual identification under a stereomicroscope. MP accumulation in gastropods was found to be affected by both species and study sites. Fibers and fragments were the most common MPs found. In conclusion, our results provide the first evidence that freshwater snails in Puerto Rico may represent an efficient pathway for microplastics from river water to estuaries.