Although collaborative governance has been presented as central in environmental management, it does not guarantee sustainable natural resources management. Due to methodological challenges and a lack of robust interdisciplinary data, few studies have linked collaborative processes to ecological outcomes. This paper contributes to that research effort by investigating whether the relative involvement of different interest groups in deliberations matters from an ecological perspective. To that end, this interdisciplinary paper links social and ecological indicators across two large French river basins in a dataset spanning 25 years. We find that the presence of different interest groups - agricultural, industrial and NGOs - during deliberations, is linked to different ecological outcomes. Most notably, the composition of present members does not play the same role depending on the type of pollution source studied (e.g. point and/or diffuse sources).