As is the case with numerous other large rivers around the world, the construction and regulation of reservoirs have altered the water and sediment regimes of the Lower Yellow River (LYR) in China, which has significantly altered the LYR. Therefore, it is crucial to examine the impact of reservoir regulation on the erosion and deposition of the LYR channel on different temporal-spatial scales, which has not been thoroughly investigated in previous studies. This study used 22 years of topographic data to examine the spatial variability of the evolution of the braided and transitional-meandering reaches of the LYR on interannual and seasonal scales. The results indicate that the LYR experienced significant siltation, which transformed into pronounced erosion after operation of the Xiaolangdi Reservoir (XLD) was initiated in 1999. The braided reach of the river downstream of the XLD had the highest annual rates of siltation and erosion, accounting for 81% and 73% of the total, respectively, within the LYR. From a seasonal perspective, the evolution of the LYR was characterized by a shift from deposition to erosion during flood season following the construction of the XLD. In contrast, the transitional-meandering reach of the LYR experienced constant erosion throughout the ∼20-year study period. During the dry season, the LYR degraded continuously, with continuous erosion in the braided reach and siltation in the transitional-meandering reach, which lies farther downstream. The water and sediment regimes in the LYR have been significantly altered by the operation of the XLD, particularly through the Water and Sediment Regulation Scheme (WSRS), a coordinated management involving XLD and two other major reservoirs in the middle reaches of the Yellow River. The water and sediment regimes altered by the operation of the XLD have primarily contributed to the shift in the evolutionary behavior of the channel. Furthermore, the regulation of the XLD also resulted in a change to the sediment budget within the LYR. The present study offers a comprehensive and systematic examination of the spatial and temporal impacts of reservoir regulation on riverine erosion and siltation processes of large rivers. The findings have significant implications for the optimization of reservoir regulation strategies to sustain channel degradation and deltaic advancement.