Environmental issues involve a wide range of actors often brought together in processes of collaborative environmental governance. Nonetheless, such actors frequently disagree on the definition of these issues. Even sharing an environmental concern does not preclude disagreements. This paper takes the concept of ecological embeddedness—so far analyzed in a single community—to explore differences of views among actors involved in collaborative environmental governance. It does so by pursuing a qualitative study of French River Basin Committees. Our findings show that Basin Committee (...) members take radically different approaches to ecological matters and therefore put forward opposing diagnoses and prognoses of their shared ecological context. We identify three dimensions of ecological embeddedness that are critical for collaborative governance, namely: ecological engagement; ecological ontology; and ecological knowledge. Our results indicate that different forms of ecological embeddedness can fuel long-lasting disagreements despite members’ shared appreciation of collaboration. This is especially so if the deliberations focus on ‘facts’—with actors pitting their ecological knowledge against one another—without facilitating discussions on ecological engagement and ontology. (shrink)