Environmental policies are characterized by a growing emphasis on participation, devolution and negotiated decision making. There is therefore a rising demand for applied simulation models which can be used as 'negotiation-support tools' to analyse the impact of the negotiation structure on the negotiated outcome. In this paper, we apply a computable non cooperative bargaining model designed to study complex real world multi-agent, multi-issue negotiation problems, to a specific negotiation process, involving water use and storage capacity. The application is on the upper part of the Adour Basin in south-western France. The case study is modelled with seven aggregate players (three aggregate farmers representing three sub-basins - upstream, midstream and downstream - two environmental lobbies, the taxpayer and the water manager), and with up to nine negotiated variables (water quotas and water prices in each sub-basin, and the capacities of three dams). Comparative statics experiments highlight a number of aspects of the relationship between negotiation structure and bargaining power.