The purpose of this new edition of the Man and River Systems symposium is to take stock of the achievements of river system studies undertaken at the whole watershed scale, and to discuss new challenges for a better understanding and management of the complex interactions between aquatic ecosystems and human activity in the watershed. Unlike the previous Man and River Systems symposium which major subject was the interactions between biological, chemical and physical processes at various scales inside the watershed, our present objective is to promote interdisciplinarity between natural and social sciences. For that purpose, the planned sessions provide a gradient of topical issues ranging from natural sciences to social sciences.