Nitrogen (N) pollution drives widespread coastal ecosystem collapse. In this paper, we argue that mangrove forests represent an undervalued natural mitigation solution for N pollution. By performing a comprehensive global meta-analysis, we reveal that mangroves remove 870 Gg N annually, which represents an economic value reaching $8.7 billion via N credit-based valuation. This value is more than 12 times higher than the annual carbon credits value derived from mangrove carbon sequestration. Despite the substantial economic importance of mangroves' N-removal capacity, it remains largely overlooked in current conservation frameworks. Moreover, we argue that N removal by mangroves has the potential of removing over 5 million tonnes of N each year under optimal conditions. We also highlight critical environmental thresholds demonstrating that this service is vulnerable: extreme eutrophication, rising mean annual temperature above 22°C, and hypersalinity all suppress mangrove N removal capacity. Our findings provide the scientific foundation to integrate “Blue Nitrogen” credits in a larger N-credit framework, offering a transformative financing mechanism for coastal water quality management that could reshape both mangrove conservation and N pollution mitigation strategies, worldwide.