The study examines the impact of groundwater nitrogen (N) legacy on water quality in four major river basins: the Rhine, Mississippi, Yangtze, and Pearl. Excessive agricultural N has led to significant N accumulation in groundwater, which persists due to slow travel times compared to surface waters. Despite regulatory efforts, N concentrations in freshwaters remain high, with groundwater acting as a major source of N to surface waters. The Rhine and Mississippi basins have seen N accumulation since the 1950s, while the Yangtze and Pearl basins entered the accumulation phase in the 1970s. Policies to reduce N pollution have not halted accumulation, highlighting the need to account for groundwater N legacy. Restoring groundwater N storage to 1970 levels will take longer in the Yangtze and Pearl than in the Rhine and Mississippi. Sustainable watershed management requires long-term strategies to address N legacy and promote sustainable agricultural practices aligned with the Sustainable Development Goals. The study uses a model to simulate N dynamics and assess future scenarios under different Shared Socioeconomic Pathways (SSPs). Results show that N delivery to surface waters will decrease in the Rhine by 2050, while the Mississippi will experience a period of increasing N delivery before decline. The Yangtze and Pearl will continue to accumulate N, with recovery to 1970 levels taking until 2050. The study emphasizes the importance of considering groundwater N legacy in environmental policies to improve water quality and manage agricultural productivity.The study examines the impact of groundwater nitrogen (N) legacy on water quality in four major river basins: the Rhine, Mississippi, Yangtze, and Pearl. Excessive agricultural N has led to significant N accumulation in groundwater, which persists due to slow travel times compared to surface waters. Despite regulatory efforts, N concentrations in freshwaters remain high, with groundwater acting as a major source of N to surface waters. The Rhine and Mississippi basins have seen N accumulation since the 1950s, while the Yangtze and Pearl basins entered the accumulation phase in the 1970s. Policies to reduce N pollution have not halted accumulation, highlighting the need to account for groundwater N legacy. Restoring groundwater N storage to 1970 levels will take longer in the Yangtze and Pearl than in the Rhine and Mississippi. Sustainable watershed management requires long-term strategies to address N legacy and promote sustainable agricultural practices aligned with the Sustainable Development Goals. The study uses a model to simulate N dynamics and assess future scenarios under different Shared Socioeconomic Pathways (SSPs). Results show that N delivery to surface waters will decrease in the Rhine by 2050, while the Mississippi will experience a period of increasing N delivery before decline. The Yangtze and Pearl will continue to accumulate N, with recovery to 1970 levels taking until 2050. The study emphasizes the importance of considering groundwater N legacy in environmental policies to improve water quality and manage agricultural productivity.