First systematic evaluation of anthropogenic debris dynamics in Sri Lankan fishery harbors: Spatial and temporal trends of macroplastic accumulation in the Western Province

Despite being identified as key pollution hotspots, debris dynamics in fishery harbors (FH); dedicated infrastructure facilities for fishing vessel operations, are poorly characterized. This study provides a comprehensive evaluation of macroplastic accumulation patterns in five FH of the Western Province of Sri Lanka over one year with covering all the seasons to examine the effects of the monsoons. Weekly sampling at 59 standardized 10 m collection points captured both stranding and floating debris across six infrastructure types. Plastic was the major pollutant type (∼85%), with single-use plastics (∼61%), considerably exceeding fishery-related plastic debris (∼10%). Infrastructure design emerged as the primary determinant of debris retention, with fully enclosed harbors accumulating 17-fold more debris than open designs. Breakwater-enclosed FH designs recorded considerably higher dynamics compared to open designs, and localized zones of high accumulation were recognized in particular infrastructure geometries. Seasonal patterns were present at some FH, with peak accumulation during the second inter-monsoon and northeast monsoon, driven by operation intensity variation rather than environmental forcing. Debris originated mainly from local sources with negligible transboundary contribution. The accumulation is governed by hierarchical controls, with infrastructure design as the primary, operation intensity as the secondary, and environmental setting as the tertiary determinant. These findings provide evidence that effective management requires infrastructure-based solutions and local waste management interventions. The infrastructure-based classification framework and evidence-based prioritization methodology are replicable tools to support policy development worldwide.