Although data is increasingly shared online and accessible for re-use, we still witness heterogeneous coverage of thematic areas and geographic regions. This especially becomes an issue when data is needed for large territories and including different nations, as, for example, required to support macro-regional development policies. Known data gaps might be closed using different approaches. Existing - but so far non accessible - data might be made available; new public sector information could be gathered; or data might be acquired from the private sector. Our work addresses a fourth option: closing data gaps with direct contributions from citizen (Citizen Science). This work summarizes a particular case study that was conducted in 2016 in the Danube Region. We provide a gap analysis over an existing macro-regional data infrastructure, and examine potential Citizen Science approaches for closing them. We consider the adoption of already existing Citizen Science projects for addressing most of the identified gaps, and suggest a particular new application for the only gap that cannot be covered in this way. This new approach addresses bioenergy as a particular field of the circular economy. On this basis we discuss the emerging opportunities and challenges for this particular way of public participation in regional development policy.