Large-scale marine protected areas (LSMPAs) are an increasingly important feature of global conservation as countries strive to meet international commitments to protect 30% of all land and sea areas by 2030. In this paper, we contribute to current interest in the imaginaries that underpin environmental governance. Drawing together work on spatial and sociotechnical imaginaries, we examine how ocean imaginaries get bound up with the rise of large, protected areas in the ocean. We develop a typology of three ocean imaginaries associated with LSMPAs, which is elaborated through an empirical analysis of the political discourse that surrounded the designation of 17 LSMPAs since 2010. We examine extracts of government statements, speeches and press releases predominantly in news article sources and government websites to consider how these ocean imaginaries are institutionally stabilised and aligned with advances in science and technology. Our analysis reinforces an understanding that the kinds of spatial imaginaries that are created for environmental governance shape and are shaped by policy and management strategies. We also find that both visions of ocean spaces and the social worlds that perceive them can be multiple. We contend that research and policy need to recognise LSMPAs and other area-based conservation measures as more-than-technical pursuits, and harness geographic scholarship to consider and enable a multiplicity of imaginaries in exploring options for environmental governance.