One of the main river management goals in the Murray Darling Basin is to strengthen the link between the river and wetland environments by augmenting natural high flow events with synchronised releases from storages. However, the volume, and timing of release, of water resources required to meet this goal is highly uncertain. An environmental planning framework is developed that generates well specified demand for environmental water and a set of high flow release rules. The framework provides clearly specified environmental objectives, giving rise to measurable performance, that are met at the lowest possible resource costs. The problem is specified as a constrained cost minimisation where the constraints define the characteristics of a successful high flow event. An optimal water release strategy is determined using a genetic algorithm. The approach is applied to a case study in the central reaches of the Murrumbidgee River and linked to a hydrological model of the entire river system. This link allows the systematic exploration of how alternative environmental objectives and release strategies affect the river system. The cost minimisation framework allows the costs of alternative strategies to be compared and options to reduce those costs to be explored.