With a Sahelian population mainly devoted to agro-pastoral and fishing activities, the drastic change in mean annual rainfall, as well as in its temporal and spatial distribution, has had dramatic consequences on water supply with serious environmental and socio-economic impacts, which has fuelled food insecurity and population migration. In this context, a project to monitor the hydrological conditions of the lake and surroundings has been put into place with the following measurements: (1) lake-level measurements combined with satellite observations, (2) river discharge measurements from its two main tributaries, (3) physical, chemical and geochemical characteristics and piezometric observations, (4) meteorological data. This observatory is supported by Chadian (University of Djamena) and French institutions (IRD, FFEM). Moreover, Lake Chad is central to the economic development of the region. Our activities contribute for efficient use of water resources at a regional level. This includes for example the Oubangui-Chari transboundary transfer of surface water, for which technical studies are under way.