This paper examines the environmental and socio-economic consequences of hydraulic infrastructural changes along the Senegal river valley and estuary. During the 1980s, two dams were built along the valley floor to facilitate hydro-electrical production and regular water supply for crop irrigation. In addition, in 2003, a breach was dug across Barbary Spit to alleviate flooding in the city of Saint-Louis, located near the river mouth. Although these structures helped regulate the river flow, they also resulted in a series of unforeseen impacts. Based on on-site measurements (topometry, water salinity, piezometry), analysis of hydrological data, field observations, and surveys with dam managers, state regional directions (Agriculture, Hydraulics, Fisheries) and local stakeholders (paddy cultivators, market-gardeners, stock-breeders, fishermen), the study examines these often unexpected consequences. The conclusion stresses the urgency of elaborating models of hydraulic management to limit as much as possible the negative consequences of the hydraulic constructions. These models should take into account not only the variety of water uses in the middle valley and delta, but also the water safety and quality (salinity) downriver from Diama Dam.