How expertise is constructed in environmental protests? We address this question by focusing on one of the best-known cases of environmental mobilization in Russia: the movement against landfill construction near the Shiyes railway station in 2018-2019. Adopting a diverse repertoire of contention which included scientific expertise, a coalition of local activists and environmental scientists was able to terminate the construction project, despite its backing by the local authorities. Instead of seeing expertise and politics as separate realms, we analyze them as jointly constructed in the course of environmental mobilization. Drawing on qualitative interviews with protest participants, fieldwork, and documents, we argue that the role of scientific expertise was not purely instrumental. Rather than using their professional authority to boost the movement’s legitimacy, environmental experts produced a study of the local environment, increasing its legibility. With scientific measurements, analyses, reports and similar ‘immutable mobiles’ at hand, activists could appeal to scientifically established ‘facts’ about the local environment and the likely adverse effects that the landfill construction . Such an alliance with the scientists’ certified expertise helped delocalize the activists’ expertise, thus making it publicly legible. Thus, the activists could bring the ‘facts’ to the court of law, using them as a source of authority superior to legal decisions that are too easily overruled in an environment of low trust to the legal system. Conversely, an engagement with the activists’ local knowledge gave a new relevance to the scientists’ certified expertise. In this way, the environmental mobilization around a particular place was inextricably intertwined with the production of knowledge about this place. Putting it more emphatically, it would have been different science, had the scientists conducted their research without the activists. Similarly, without scientific expertise, the activists’ repertoire of contention would have been different, producing a different form of political action.