The development models of contemporary Western societies continue to exert increasing pressure on ecosystems. The ecological crisis also has major social implications, manifesting in issues of environmental justice, social inequalities, and the lack of legitimacy in political decisions. In this context, citizens' movements are becoming increasingly prevalent, spreading across the world and playing a prominent role in the public sphere. These citizens' movements may represent an alternative societal response to the ecological crisis, particularly by compelling developers to better account for environmental concerns in their projects. Studying these movements can thus offer insights into their role in shaping the evolution of land-use practices both at the level of project developers and the institutions that provide the regulatory frameworks. Our research aims to better understand the formation of public preferences for thinking future land-use scenarios. Applied to the case study of the Rhône à Sète canal located in Southern France and using deliberative approaches, our results highlight the crucial role of the co-construction of preferences in improving citizens' ecological knowledge and selecting land-use scenarios with minimal environmental impact. It is essential that planners have a better understanding of ecological social demand in order to guide their planning and, more generally, public environmental policies.