Insufficient observational evidence of hydrological parameters and, more importantly, river discharge at the global scale is a major impediment for progress in hydrological modeling. As the data provision from in situ gauge networks is deteriorating, satellites come to the rescue. Although spaceborne sensors offer a synoptic and global view by their very nature, they do have their own limitations for a full catchment river discharge estimation. The SWOT mission aims to alleviate the limitations and significantly improve spaceborne estimates of river discharge. The SWOT mission will provide measurements of water surface elevation, river width and slope, through which discharge can be estimated for river widths down to 50–100 m. This project aims to greatly improve river discharge estimation, by innovative modeling of results from SWOT and existing satellite altimetry (water level) and satellite imagery (surface area). To this end, an Ensemble Kalman-Filter (EnKF) based method will be developed to best estimate river discharge at full-catchment scale (applicable to global scale), which can deal with non-stationarity due to man-made interference, natural behavior or climate change. Moreover, within the developed EnKF, an ensemble of SWOT discharge values from different existing discharge estimation algorithms are ingested into the observation equation, leading to an assimilated (combined) estimation of river discharge at full catchment scale.