This study focused on investigating the occurrence, quantification, and the spatial and temporal distribution of plastics in coastal surface water from 12 coastal regions in southern part of Sri Lanka. The overall average densities of macroplastics and mesoplastics were recorded as 0.23 and 0.33 items/m³, respectively. Sampling locations had no significant difference (p > 0.05) on total microplastics (MPs) density (overall mean MPs density: 17.45 ± 3.35 items/m³). MPs debris of less than 1 mm size consisted of >45% of the total number of MPs, whereas the maximum size of microscopically observed plastic debris was 11.04 mm, a filament. Filaments were the most common MPs followed by films. Relatively, blue-colored MPs were highly abundant in this coastal line. The type of MPs was further confirmed by Fourier-Transform Infrared (FTIR) method. Potential plastic pollution factors are hydrodynamics and man-made activities like unsustainable harbor operations, fisheries, and tourism. More attention is needed to reduce plastic pollution regionally.