Coastal-water hypoxia is increasing globallydue to global warming and urbanization, and the need todefine management solutions to improve the water quality ofcoastal ecosystems has become important. The lower tidalGaronne River (TGR; southwestern France), characterizedby the seasonal presence of a turbidity maximum zone(TMZ) and urban water discharge, is subject to episodichypoxia events during low river flow periods in the summer.Future climatic conditions (higher temperature and summerdroughts) and increasing urbanization could enhance hy-poxia risks near the city of Bordeaux in the coming decades.A 3-D model of dissolved oxygen (DO) that coupleshydrodynamics, sediment transport and biogeochemicalprocesses was used to assess the efficiency of differentmanagement solutions for oxygenation of the TGR duringsummer low-discharge periods. We ran different scenarios ofreductions in urban sewage overflows, displacement of urbandischarges downstream from Bordeaux and/or temporaryriver flow support during the summer period. The modelshows that each option mitigates hypoxia, but with variableefficiency over time and space. Sewage overflow reductionimproves DO levels only locally near the city of Bordeaux.Downstream relocation of wastewater discharges allows forbetter oxygenation levels in the lower TGR. The support ofow river flow limits the upstream TMZ propagation anddilutes the TGR water with well-oxygenated river water.Scenarios combining wastewater network management andlow-water replenishment indicate an improvement in waterquality over the entire TGR. These modelling outcomesconstitute important tools for local water authorities todevelop the most appropriate strategies to limit hypoxia inthe TGR.Read less <