Plastic pollution and non-native species have become major threats to freshwater ecosystems due to human activity. The Asian clam (Corbicula fluminea), a widespread invasive species in Europe, has been identified as a potential contributor in the bioaccumulation and trophic transfer of microplastics. This study examined the occurrence and accumulation of these pollutants in C. fluminea, correlating these pollutants with macroplastic contamination of the banks and sediments of five rivers in northern Portugal (Cávado, Homem, Lima, Minho, and Neiva), with varying degrees of pollution. Samples of macroplastics, sediment, and bivalves were collected and analyzed using Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy for particle characterization according to colour, size, and polymer type. Results indicated that polyethylene was the most prevalent polymer and transparent particles were the most abundant, with particles sized 0.3-1 mm being the most abundant. No significant relationships between the percentage of organic matter and microplastic abundance (in sediment or bivalves) were found by the statistical analysis. The findings underscore the role of C. fluminea as a significant bioaccumulator of microplastics and a potential vector for their transfer through the food web. This reinforces the importance of this bivalve in the dynamics of plastic contamination in freshwater ecosystems and highlights the urgent need for further research into the ecological consequences of this interaction.