This article is an attempt to address the issue of territory by an emerging perspective in sociology: the study of cognitive and epistemic dimensions of governance and participatory democracy. In order to examine the integration of the inhabitants’ representations and of the lay knowledge in decision-making, it focuses on the collective work of objectification of the territory necessary to the collective management. Analyzing the epistemic and cognitive properties of objectification, the author identifies two processes limiting the integration of lay knowledge and local representations to the definition of the project territory: the dynamic of epistemic relations and the realization of the organizational learning by creating rules of management. The article relies on a case study corresponding to the collective water management in the Camargue (France, Bouches-du-Rhône) that necessitated the sociological inquiry of a participatory commission conducted from 2009 to 2012.