The aim of this study is to achieve an understanding of the collective management of wetlands by landowner associations, in order to reflect on their role and position within the new wetland resource governance system, initiated by the recent institutional reform in France. Proposals from self-governance institutions for natural resource management and social capital studies inform the analytical framework. Two survey phases among the chairs and members of associations that currently manage the riparian marshes of the Gironde estuary are the basis for an empirical study. The results reveal that half of the landowners sampled will default. However, neighbourhood and community-based social capital as well as the close involvement of the chairs of the associations are the key elements of the collective management of water-level and wetland resources. We then argue that informal and flexible collaboration between small associations should be the governance mode for the collaborative management of wetlands.