The Barmah and Millewa Forests contain extensive areas of Eucalyptus camaldulensis (river red gum) forest growing on a flood plain of the River Murray. In the past, under natural conditions, the forests were extensively flooded in winter/spring of most years, often for two or more months' duration. Indeed, the best quality forest has developed on those areas most regularly flooded. However, following construction of Lake Hume the river flow has been regulated since 1934 with the effect of reducing winter/spring flows and increasing summer/autumn flows for irrigation purposes. As a consequence, the frequency and duration of winter/spring flooding of the forest has decreased and also localised and prolonged flooding of the forest in summer/autumn has led to deterioration and death of some stands. With completion of Lake Dartmouth on a major tributary, the Mitta Mitta River, the effects of river regulation will be accentuated. A summary of river flow data from 1886 to 1984 is presented, showing natural flows from 1886 to 1933 and from 1934 to 1984 a comparison of actual regulated flow against the estimated natural flow without the effect of storages. In addition, a detailed analysis is given of the impact of river regulation on the effectiveness of forest flooding. A joint study and works program has been undertaken by the River Murray Commission and a States Working Party to develop strategies for river management that will meet the needs for irrigation water as well as providing for more regular watering of the forest in winter/spring, and without significant flooding in summer/autumn, in an endeavour to maintain the forest ecosystems in a healthy condition.