The objective of this study is to present the morphology of the bottom and to characterise the filling dynamics in the downstream sector of Buyo lake. A bathymetric survey carried out in March 2021 and the use of an old topographic map of the Buyo hydroelectric development dated 1980, allowed to apprehend the impact of the hydrosedimentary processes on the morphological evolution of the Buyo lake bottom. The analysis of the topo-bathymetric maps revealed that the downstream sector of Buyo Lake presents a rather irregular relief with depths ranging from 0 to 26 m. The greatest depths are located at the level of the flood spillway and the shallowest depths in the vicinity of the water intake. The 3D map of the lake shows the presence of depressions and shallows. The maximum depth was 24 m in 1982 and will be 26 m in 2021. In some places, the depressions of 4 and 22 m that were recorded in 1982 are 6 and 16 m respectively in 2021. The volume of deposition over the last 39 years (1982 to 2021) is estimated to be about 6,130,297.08 m³ of sediment with a filling rate of 68 cm/year. The analysis of the main channels revealed bathymetric profiles of intermediate and « V » morphology.