<p>Terrestrial water enters the sea through estuaries as buoyant plumes. While the near-field water plume has been extensively investigated via campaign data and/or ocean modeling, the seasonal migration and spatial extent of the extended water plume remain poorly understood. Recently, global detection of Earth’s mass migration has been achieved via satellite gravimetry, in particular the terrestrial water mass migrating to the ocean. Through causality-validated cross-correlation analysis between runoff and satellite gravimetric-derived water height corrected by atmospheric and oceanic mass variations without correcting runoff forcing over the Sunda Shelf Sea (SSS), we found that the extended water plume during summer first migrates northeast to ∼12°N, then clockwise along Borneo’s coast to southwest of the SSS. Its transit pattern during winter yields a shorter duration to the northeast and southwest, and a longer duration to the middle of the SSS than those during summer. El Niño-Southern Oscillation (ENSO) mainly influences the winter transit pattern. Using sliding three-year data windows (2003–2015) for determining the transit pattern every year, we attribute the accelerated and retarded SSS transit patterns to prolonged La Niña and alternating ENSO events, respectively. Generated from the addition of altimetric-inferred geostrophic current and wind-driven Ekman current at the ocean surface, the simulated transit patterns show consistency with satellite gravimetric-determined winter transit patterns. Validation with isotope-estimated ages confirms improved accuracy over previous studies.</p>