Compound Drought and Saltwater intrusion Events (CDSEs) happen when rivers face both drought and saltwater intrusion at the same time, making things worse. A new index called SDSI was created to track these events in six major river estuaries. The SDSI was better at showing CDSE severity than the old index. Different estuaries had different trends in CDSE severity. Some estuaries had a high chance of CDSEs, with the Murray Estuary having the longest and most severe events. Saltwater intrusion was a big factor in CDSE severity, especially in the Orange Estuary.