National policy styles and path-dependencies are affecting the abilities of Baltic Sea countries to deliver on their commitments under the Helsinki Convention. This article synthesizes evidence and insights from studies relating to the provisions on agricultural nutrient management, a main source of marine pollution. We contend that governments that are strongly concentrated vertically, while fragmented horizontally, lack capacity including with respect to informal institutions that can leverage implementation. As a stocktaking of institutional impediments to sustainable development, our analysis has wider relevance for other international agreements with Baltic Sea countries involved.