Given the extensive challenge of marine litter faced by coastal ecosystems, this article aims to illuminate an innovative form of environmental caretaking that builds upon a newly established concept of relational environmentalism. Relational environmentalism is a movement of individuals who purposefully interact with each other and with external bodies in a variety of dynamically developing ways to affect the perceptions, motivations and practical actions for the caretaking of endangered natural environments. As a theoretical contribution, the article conceptualizes eight categories of relational environmentalism: inviting, informing, coaching, norm enforcing, politicizing, mobilizing, intergeneralizing, and bridging. By means of a social media content analysis and primary data from the “Marine Environment Patrol” Facebook site, the article provides the first evidence on what relational environmentalism is and how it is institutionalized in the case of leisure- and tourism-based volunteering to collect marine litter. Furthermore, the article shows that successful campaigning and environmental patrolling in coastal recreation and tourism is a matter of building alliances and exchanging logics across a variety of boundaries and that it depends on a gradual intensification and diversification of communicative and mobilizing measures.