With the HydroWEB service (http://hydroweb.theia-land.fr), LEGOS has been developing since 2003 a database of water level variations on lakes and rivers around the world based on satellite altimetry. Several thousand virtual stations are monitored and available in HydroWEB, in operational mode (real-time update) or in delayed mode. More than 150 lakes are also monitored, some in operational mode. In addition, changes in extent and volume are also measured for many of them.

The HydroWEB service is intended to provide users, scientific or otherwise, with information on state variables related to the hydrology of continental surfaces from various satellite data. Most of these variables are part of the list of Essential Climate Variables (ECVs) established by the Global Climate Observing System (GCOS).

This service is hosted on the THEIA national cluster platform. It is operated by the company CLS under the coordination of LEGOS, IRD and CNES.