<p>The occurrence of harmful algal blooms in Jinyang Reservoir, South Korea, has raised public concern, particularly among residents who depend on the reservoir as a drinking water source. To address these concerns, the present study investigated the total P (TP) release behavior of sediments from Jinyang Reservoir and its tributaries, namely the Deokcheon and Gyeongho Rivers, focusing on the roles of indigenous microbial communities and sedimentary redox processes. Sediment analyses revealed distinct microbial profiles across the investigated sites: iron-oxidizing bacteria dominated in the Jinyang Reservoir sediments, while sulfate-reducing bacteria were more prevalent in the Deokcheon and Gyeongho River sediments. These microbial differences may have influenced sediment redox conditions and indirectly affected Fe-associated P mobilization. Elevated pH further enhanced TP release, underscoring the contribution of alkaline conditions to P mobilization. Mitigation experiments demonstrated that treatments with an oxygen-releasing agent (CaO₂) and loess particles effectively suppressed TP release. However, additional studies are required to assess their long-term efficacy and ecological consequences. Overall, our findings offer valuable insights for developing eutrophication control measures in Jinyang Reservoir and its tributaries. Implementing targeted interventions based on these results may help reduce nutrient loading and alleviate eutrophication risks in reservoir systems.</p>