This talk explores the marshes of the north shore of the Lower Loire. These marshes, at the interface between fresh and salt water, have been the subject of an in-depth ethnographic survey for five years by a multidisciplinary team of researchers. Constituting environmental commons, managed and used by local communities, these marshes are facing many changes. These mutations, with multiple origins, disturb the balance between humans and non-humans. Adaptive strategies are emerging to protect resources, uses and heritage, in an attempt to continue the centuries-old perpetuation of certain traditions. After a methodological and conceptual framework, this paper presents what emerges from this field, a real complex social-ecological system of interfaces, and to decipher the processes at work between Nature and Culture. Navigating from traditional ecological knowledge to heritage through the fuzzy sub-category of intangible cultural heritage, this territory is thus a veritable laboratory of the changes at work within European wetlands. The ethnographic approach allows a long-term immersion in the community, and the crossover study between social and natural sciences allows a conceptual cooling, able to propose an objective hindsight of analysis.