The optimal management of multi-purpose reservoirs is particularly challenging for event-driven real-time operation to ensure a predictive planning and determine the best possible operational strategy. This requires the application of an optimal flow forecast for the river basin as well as knowledge of the effects of control instructions on the flow dynamics and on the achievement of operational objectives. The decision support tool for the management of the Edertalsperre presented in this paper is based on free software products supporting the determination of the required reservoir release. Outcomes are the most effective solutions to fulfil the pre-specified multi-purpose operational objectives. Based on these results, upcoming conflicts of objectives can be analysed efficiently. In combination with the users' practical experience, a feasible control instruction may be derived.