The city of Perreux-sur-Marne has rethought its entire relation to its river, considering it as a major environmental, social, urban and political issue. The project aims at bringing back both the people and other species of plants and animals to the banks of the river Marne, by softening the water and urban edges. Concrete protections are turned into vegetal engeneering, and overflood is accepted, widening the spectrum of environements.