Previous studies have identified a strong link between climate variability in Australia and the El Ni¿o--Southern Oscillation (ENSO). This paper describes the development and use of a seasonal streamflow forecast model based on an optimal linear combination of forecasts derived from climatology, persistence, the Southern Oscillation index (SOI), and equatorial Pacific sea surface temperatures (SST). The model builds on the work of the Australian Bureau of Meteorology and that of other researchers who have investigated southeast Australian rivers. The model is tested using 66 years of unimpaired streamflow data from 10 eastern Australian catchments. Results from testing the model further support the ENSO-hydroclimate link, showing that eastern Australia generally receives below normal streamflow during El Ni¿o conditions and above normal streamflow during La Ni¿a conditions. In southeast Australia the SOI is a better predictor for July--September and October--December streamflow and the SST a better predictor of January--March and April--June streamflow. For many of the seasons and stations, the skill associated with the cross-validation forecast is better than that drawn from the baseline condition of climatology. ¿ 1998 American Geophysical Union