Over the past half-century of evolution in the Yangtze River-Dongting Lake water network, the regulating and storage function of Dongting Lake over the Yangtze River and the Xiang, Zi, Yuan, and Li Rivers in Hunan has gradually shifted from flood retention and sedimentation to flood regulation and sediment replenishment. This transition marks a new phase in the relationship between rivers and lakes, necessitating updated perspectives for their governance and protection. This study, based on comprehensive prototype observation data of the Yangtze River main stream and the Dongting Lake water system, thoroughly analyzes the developmental process, distribution characteristics, and driving factors of sedimentation to sediment replenishment in Dongting Lake. It reveals the macroscopic response of hydrological conditions (flood and dry seasons) in the lake region to changes in sediment deposition status. Results indicate that Dongting Lake has sequentially undergone three developmental stages: the sediment retention weakening phase, the sediment retention stabilization phase, and the sediment replenishment enhancement phase. Sediment deposition progresses from west to east, while sediment replenishment moves from east to west, maintaining the seasonal pattern of deposition during flood periods and replenishment during non-flood periods. Sediment replenishment is primarily dominated by extremely fine particles, which do not contribute to bed formation in the Yangtze River main stream but facilitate the replenishment of nutrient materials. High sediment inflow and weak hydrodynamic conditions are the primary causes of sediment deposition. The sustained decline in sediment concentration of lake inflow, driven by the operation of controlling reservoir groups and soil conservation projects, serves as the core driving factor for sediment replenishment. However, the level of sediment replenishment in the lake region remains low and shows limited potential for further development. Sediment deposition is one of the main factors behind the widespread elevation of the highest water levels in the lake region prior to the impoundment of the Three Gorges Reservoir. The water replenishment regulation of the Three Gorges Reservoir downstream of the dam struggles to mitigate the declining trend of the lowest water levels in the Dongting Lake region. While changes in sediment deposition status will improve flood control conditions in Dongting Lake, the hydrological situation during dry seasons in the lake region is becoming increasingly strained.