Abstract The Baltic Sea environmental protection regime is an example of a close science-policy interface. At the same time, however, research on international environmental regimes increasingly admits that experience-based knowledge may serve as a useful instrument to facilitate effectiveness of environmental management. Moreover, in an 'age of expertise', questions about the relation of expertise to citizen participation in policy-making are perhaps more relevant than ever. Using expert interviews and policy documents as the main data, the paper examines the close relationship between the scientific community and the international regime and assesses the possibilities for public engagement and, consequently, integrating experience-based knowledge into the work of the regime. In the paper, it is analysed how the scientific community in Finland defines the problem of eutrophication of the Baltic Sea vis-a-vis the transnational policy regime; also spatial and temporal scale frames are identified. Results indicate that the dominant problem and scale framings emphasize the ecosystem-wide ecological and scientific-technical nature of the problem and its solution, which restricts the possibilities of public engagement and integration of experience-based knowledge into management. Finally, the paper discusses the pros and cons of management approaches based on scientific vis-a-vis experience-based knowledge.