This article uses social movement theory to explore how decentralized stakeholder governance can be fostered at the river basin level in contexts where local actors lack incentives to participate. Based on two Brazilian river basins where efforts to promote collaboration among state, civic and private organizations were successful, it emphasizes the importance of building collective identities revolving around river basin issues and groups. It shows how leadership and initial collaborative practices help build such identities, through reframing ideas about problems and solutions and through building basinwide networks, trust among stakeholders and social and political recognition.