International aid projects in post-communist countries were meant to support environmental protection during the transition period and to introduce new standards of environmental governance. While the outcomes of the World Bank biodiversity project in the Belavezhskaya Pushcha National Park in Belarus were evaluated positively after its delayed completion, an assessment using the same criteria 10 years later questioned its long-term effectiveness. This paper links current project outcomes with the implementation process, and uses this knowledge to deduce lessons for designing and implementing future international initiatives in Belarus and other post-communist contexts. There are four interlinked and project-specific reasons for the observed unsustainability of project outcomes are identified: (1) the predominance of the natural sciences, (2) an unbalanced representation of actors within the hierarchical system of governance, (3) powerful implementation by official high-level actors, and (4) insufficient knowledge of participatory methods and principles of multi-level governance. In order to introduce new standards for environmental governance, international aid projects should (1) streamline communications between the actors at different scales, including donor organizations, local agencies and stakeholders in the receiving countries; and (2) use ongoing project and, in particular, process assessment to reflect on the project progress to achieve longer term effectiveness of project outcomes.