This talk follows a nascent civil society group in Lebanon run by young marine biologists organizing a campaign against invasive fish species in the Lebanese waters. Populations of lionfish (pterois), native to the Read Sea and Indian Ocean, have expanded at a rapid pace in the waters of Eastern Mediterranean since around 2015, and have raised concern in countries across the sea. The lionfish are seen as arriving from the Red Sea through the Suez Canal, possibly facilitated by rising water temperatures related to the climate change allowing for the fish to advance to new areas. The increasing presence of lionfish in Lebanese and Mediterranean waters is consider a threat to local marine life and indigenous fish populations. Based on ethnographic fieldwork among volunteer-run groups on the Lebanese coastline, I follow young marine biologists and other volunteers in their campaigning against the lionfish. I discuss how the lionfish, categorized by marine science as invasive, was conceptualized by the group of marine biologists through their environmental advocacy work. I examine how "fighting" the invasive species was incorporated as part of their environmental campaign work on the Lebanese littoral. Combining transnational knowledges of marine biology and non-governmental advocacy, the lionfish-encounter brought the young scientists and activists in diverse activities and entanglements across the Lebanese coastline. A central part was their campaigning for 'oceanic literacy' – a concept borrowed from global marine science pedagogy – a specific educational pursuit of changing the relationships of Lebanese with the sea. Through this ethnography, the paper asks: As the lionfish was made known, and edible, to the Lebanese public, what kind of new oceanic entanglements were brought forth? What ’work’ did the category of invasive, and its playful associations with enemy-ness, do in changing the Lebanese public knowledge of the sea? How did the categorization of the lionfish as non-native in the Mediterranean affect environmentalist understandings of the species and its effect on the local ecosystems? And in what ways did this specific encounter with the Lessepsian migrations figure in changing relationships to the sea in Lebanon?