About two-thirds of global freshwater comes from surface waters like tidal estuaries, which are increasingly affected by saltwater intrusion due to factors such as droughts, sea-level rise, river floods, tides, storm surges, and human interventions like channel modifications and water management. However, the combined impact of these factors—especially during prolonged drought—remains poorly understood. This knowledge gap has gained public attention through reports of salt-contaminated drinking water in tidal rivers. The SCOR Working Group 172 “SALTWATER” aims to address this issue by advancing interdisciplinary research and developing a global synthesis. We welcome contributions on estuarine salt intrusion using theoretical, observational, modeling, or machine learning methods. We invite contributions highlighting new findings on estuarine salt intrusion processes, using theoretical, observational, numerical, statistical or Machine Learning approaches.