In the context of intensification of flood risks, Nature Based Solutions constitute an interesting approach to conciliate population’s protection and biodiversity. While this recently emerging concept has been the subject of studies in social sciences, there is no work yet with a social representation approach. In this work, we propose to study Nature Based Solutions for flood risk management through the prism of social representations and how they frame the implementation of Nature Based Solutions projects in the field (obstacles and levers). We interviewed 19 flood experts who can be divided into two groups regarding Nature Based Solutions: theorists and practitioners. We studied their discourses using two types of analyses: a lexicometric analysis of the similarities and a thematic analysis. The results showed that Nature Based Solution is a social representation object in its complexity, the polarisation it creates and its technicality. The two groups of participants have different representations. The practitioners may consider the Nature Based Solutions as "greenwashing" since they are presented as new and innovative, while the theorists contrast their Nature Based Solutions’ vision with a "grey" vision influenced by French civil engineering culture and a need to control ecosystems. Both groups agree that Nature Based Solutions thinking is about "leaving more room for nature", which echoes Dunlap’s New Environmental Paradigm. Moreover, the results suggest that the expression “Nature Based Solutions” is not well suited to all actors. We encourage using the expression “vegetal engineering” which may provide an opportunity to reconnect with the techniques applied in the field. It also enhances the value of ancestral knowledge, which allows the general public to better connect with the concept.