Local participation, especially in natural resource management, has been promoted as a key strategy in the quest for sustainable development. Community-based Natural Resource Management (CBNRM) is an approach that has generally been promoted as an institution that genuinely includes and empowers ‘local people' in natural resource use and management. This paper examines how local participation in conservation projects works in practice by drawing on concepts from institutional and actor-oriented theories and applying a case study approach to examine community-based mangrove management at Jozani-Pete, Zanzibar. Here CBNRM became embedded within a conservation agenda that resulted in conflict, resistance, frustration and uncertainty amongst community members. The paper offers insight into how exogenously initiated CBNRM projects have difficulty gaining traction unless they both address existing power relations and deliver on promises of material benefits. If they fail to do so the experience of the Jozani-Pete case study suggests that CBNRM may work to further marginalize already marginalized people.