While public participation has become a regulatory requirement, we question the legitimacy and the place given to civic knowledge in the participatory management of water territories. To answer these questions, this article presents a participatory research project involving residents of the Dordogne River. Several tools have been mobilized (workshops, maps, interviews) to engage public participation, identify, and understand the construction of civic knowledge. All of this research was filmed and resulted in the making of a film. The screening sessions allowed for further debate. The analysis of the data produced highlights a plurality of knowledge and a diversity of uses of the river that we present in the article. Nevertheless, the feeling of attachment to this space contributes to the construction of a common riverine identity. Faced with a management dominated by “expert knowledge,” the use of civic knowledge and its mobilization in participatory tools would politicize issues concerning the development of the Dordogne more effectively. Legitimate consideration of this knowledge would ensure the appropriation of water territories by local populations.