Plastic debris has become one of the most pressing global environmental pollutants, infiltrating aquatic ecosystems from freshwater sources to marine environments. Its persistence, buoyancy, and fragmentation into micro- and nanoplastics have profound ecological consequences, altering habitat structure and degrading water quality. These contaminants threaten aquatic biodiversity through physical ingestion, entanglement, and toxic leachates, disrupting food webs and impairing fish health, growth, and reproduction. Consequently, plastic pollution directly undermines sustainable fisheries, reducing productivity and posing risks to food security and human health through bioaccumulation and trophic transfer of microplastics. This chapter critically examines the sources, transport pathways, and ecological impacts of plastic debris in aquatic systems, emphasising its influence on habitat integrity and fishery sustainability. It also highlights recent scientific findings on the interactions between microplastics and fish physiology, as well as the impact on ecosystem processes. This discussion highlights the pressing need for integrated waste management strategies, policy interventions, and global cooperation to reduce plastic inputs, promote circular economy principles, and ensure the resilience of aquatic environments and fisheries resources.