Résumé
Many canals were built during the 19th century to satisfy multiple uses, which have since highly changed, calling into questions about their function. This article assumes that these old hydraulic works can help the territories to adapt, if reforms of their hydraulic, economic and institutional management are carried out at the same time. It illustrates this assumption and its consequences with the Neste Canal (in South France). The evolution of the multiple uses and the decrease in the flows derived over the last 70 years are described conducting to a structural imbalance of its economic model. Its future depends on the political recognition of its contribution to the minimum water flows of the rivers of Gascony, the introduction of a payment for this ecological function, and changes in the hydraulic regulation system to satisfy this last function previously managed as a hydraulic constraint.