Coastal ecosystems (mangrove forests, seagrass beds, coral reefs) provide vital services (eg, fisheries’ foundations and coastline stability). In Southeast Asia, nonetheless, the ecosystems are under severe pressure from developments (especially aquaculture), overexploitation, climate change, and cryptic degradation from pervasive exposure to various anthropogenic water pollutants. This chapter describes major coastal pollutants (heavy metals, "wastewater nutrients," antibiotics, and others) and their specific sources (agriculture, industries, aquaculture). It reviews the coastal ecosystems' varied sensitivities to pollution hazards. It then examines options to contain/capture and treat wastewater, especially the utility of natural and constructed vegetated wetlands as upstream "greenbelt" buffer systems. Finally, it focuses on the question to what degree mangroves—as a last "line of defense"—can provide pollution mitigation services. Mangroves are valuable filters for certain types of "incidental" water pollution. Strategies to reduce/mitigate pollution at or near the emission source, however, deserve the main attention for effective coastal pollution management.