Contamination of freshwater ecosystems by microplastics has become a significant global issue. This study investigates the abundance, distribution, and characteristics of microplastics in the surface water and sediments of the Densu River during both wet and dry seasons. Surface water and sediment samples were collected from ten (10) sites in the Densu River and processed using density separation with NaCl solution. Microplastics were identified under a Motic SMZ-71 stereomicroscope, and FTIR analysis was conducted to determine the polymer composition. Land use/land cover (LULC) analysis was conducted using the ESA WorldCover 2021 dataset, and Principal Component Analysis (PCA) was applied to evaluate the relationships among catchment land-use composition, hydrological conditions, as well as microplastic abundance and characteristics. Sampling was conducted in June 2024 (wet season) and December 2024 (dry season), with a total of 120 samples collected. The surface water had a mean microplastic abundance of 1.63 ± 0.95 particles/L during the dry season and 2.57 ± 1.42 particles/L during the wet season, showing no significant difference between the seasons ( p = 0.101). The difference in mean microplastic abundance in sediment was 20.67 ± 8.55 particles/kg dry weight (dw) in the wet season and 29.67 ± 11.60 particles/kg during the dry season. Fragments and fibres predominated among microplastic forms, while polyethylene and polypropylene were the primary polymer types identified in surface water and sediments across both seasons. Microplastics of diameter < 1000 μm constituted 85.72% in surface water during the wet season and 82.02% in the sediment during the dry season. The Pollution Load Index values, ranging from 1.0 to 4.14, indicated low risk levels of microplastic contamination in surface water and sediments across the sampling sites. Natural vegetation dominated the river catchment (78.40%), while built-up areas accounted for 16.23%. PCA indicated that spatial variability in microplastic distribution was associated with catchment land-use composition, polymer composition, particle characteristics, and hydrological conditions. Sites with higher urban influence were associated with potential anthropogenic inputs, whereas agricultural areas suggested runoff-mediated transport pathways. These findings emphasise the need to improve the management of plastic initiatives and develop long-term mitigation programmes to address the microplastic pollution in the Densu River and other freshwater bodies.