There have been many authors who have examined the question of participation and the extent of its influence in water management. The empowerment of stakeholders in decision-making processes has been a major issue in this field. The involvement of different types of public actor can be enacted in different manners and depends strongly on how the decision-making pro- cess works in reality, on the extent to which actors are truly able to be active in this new partic- ipatory process and on who holds the responsibility for its implementation. These variables underline the various obstacles that face the implementation of a true intersectoral participa- tion, one that successfully involves all water users. This article uses the case study of the Rhone River to explore the issues of public participation within a transboundary river where no inter- national basin organization has been able to successfully regroup the different initiatives. I consider this example to be particularly interesting, as it allows for a comparison between dif- ferent arenas that are not linked, yet are active within the same river basin. In acknowledgement of the increasing number of participatory initiatives, the article highlights and considers the dif- ficulties associated with the implementation of participation within and between fragmented participation arenas. This article proposes an analysis of the different participation arenas of the river through the lens of three analytical variables: social efficiency, substantial efficiency and procedural efficiency. The focus turns to the impact of such a participation structure and questions the increased number of arenas in which stakeholders participate regarding water- shed management.