The resource management problem for the Middle Platte ecosystem is that there is insufficient water available to meet both in-stream ecological demands and out-of-stream economic needs. This problem of multiple interest groups competing for a limited resource is compounded by sharp disagreement in the scientific community over endangered species needs for in-stream flows. In this paper two game theory models are developed for addressing this resource management problem. Model I was designed as a second price sequential auction with repeat bidding and can be used for determining how much environmental water each state will provide and at what price. Model II was designed as a utility based multilateral bargaining model and can be used for determining how much water to allocate to environmental needs, given the supply costs from Model I. Empirical results are presented for Model I only. The results suggest that the use of game models can improve the prospects for reaching a resource management agreement. The willingness of states to supply environmental water is enhanced if the bargaining process is structured to disallow cheating and provide for political compensation.