Coastal　reservoirs　could　be　used　to　store　freshwater　in　coastal　cities,　but　the　conversion　of　coastal　reservoirs　to　freshwater　reservoirs　is　relatively　time-consuming,　and　coastal　reservoirs　are　facing　a　risk　of　salinization.　Taking　Zhuyu　Lake　as　the　research　object,　the　Spatio-temporal　variations　of　water　salinity　under　different　seasons　were　investigated　using　the　field　survey　and　modeling.　The　influencing　factors　of　the　water　salinity　of　the　reservoir　were　analyzed　to　discover　the　variation　mechanism.　The　results　showed　that　the　disturbance　of　overlying　water　is　the　most　significant　factor　affecting　the　salt　release　of　sediment,　and　salt　release　was　increased　by　63.3%　with　the　disturbance.　The　depth　of　the　overlying　water　and　the　salt　content　of　bottom　sediment　also　significantly　affected　the　release　of　salt,　with　maximum　enhancement　by　23.1%　and　45.6%,　respectively.　The　microbial　content　in　the　bottom　mud　played　an　essential　role　in　maintaining　the　salt,　and　inhibiting　the　microbial　activity　could　enhance　the　release　of　salt　by　35.7%.　Therefore,　disturbing　the　sediment　by　using　disturbance　ships　or　aeration　devices,　and　the　establishment　of　a　long-term　periodic　plant　harvesting　belt　could　be　used　in　the　coastal　fresh　reservoirs　desalination　and　slowing　down　the　salinization　of　fresh　reservoirs.　©　2021　The　Institution　of　Chemical　Engineers