The　construction　of　reservoirs　leads　to　the　transition　of　rivers　to　lakes　and　reservoirs，leading　to　a　global　environmental　issue　known　as　eutrophication.　Excessive　endogenous　pollutant　loads　further　exacerbate　the　risk　of　reservoir　eutrophication　and　water　quality　degradation.　Due　to　the　lack　of　analysis　of　endogenous　phosphorus　pollution　in　sediments　of　subtropical　river-type　reservoirs，a　study　was　conducted　to　investigate　the　geochemical　coupling　of　phosphorus（P）with　iron（Fe），manganese（Mn），and　sulfur（S），as　well　as　the　speciation，migration，and　release　mechanism　of　phosphorus.　The　high-resolution　distribution　of　P，Fe，Mn，and　S　in　the　riverine　deep-water　reservoir（Shuikou　Reservoir）was　measured　using　diffusive　gradients　in　thin　films（DGT）and　high-resolution　dialysis（HR-Peeper）.　The　results　showed　that　the　NaOH-P（NaOH　extracted　P）was　the　main　form　of　phosphorus　in　sediments；iron-bound　phosphorus　was　a　key　factor　controlling　phosphorus　release　from　sediments；water　and　sediments　were　highly　nutrient-rich，and　endogenous　phosphorus　pollution　was　serious　in　sediments　of　Shuikou　Reservoir；in　vertical　profiles，P　in　sediments　correlated　significantly　and　positively　with　Fe，S，and　Mn.　The　reduction　and　dissolution　of　Fe/Mn　oxides　and　sulfate　reduction　were　conducive　to　the　release　and　activation　of　phosphorus.　The　positive　diffusion　fluxes　of　P，Fe，Mn，and　S　at　the　sediment-water　interface　indicated　that　the　sediments　would　release　these　materials　to　the　overlying　water.　During　the　opening　and　release　of　reservoirs，convection　temporarily　break　stratification，resulting　in　a　higher　release　flux　of　endogenous　phosphorus　compared　to　most　natural　shallow　lakes　and　reservoirs.　These　findings　underscore　the　importance　and　urgency　of　addressing　endogenous　phosphorus　pollution　in　riverine　reservoirs.　©　2024　Science　Press.　All　rights　reserved.