Environmental peacebuilding refers to efforts aimed at building more peaceful relations through environmental cooperation, natural resource management, climate change adaptation and disaster risk reduction. It is an emerging research field with the potential to integrate various lines of environmental security research. Environmental peacebuilding practices have also been widely applied by conservation, development and peacebuilding practitioners, including those working at the grass-roots level in local communities. While its positive effects are considerable, environmental peacebuilding can also have adverse effects. This dark side of environmental peacebuilding has received little attention and remains under-researched. Based on evidence from a broad set of cases located in various world regions, I discuss these adverse effects within six categories (the “six Ds”): depoliticisation, displacement, discrimination, deterioration into conflict, delegitimisation of the state, and degradation of the environment. Only with sufficient consideration of these adverse effects, their interactions and the associated risk factors will environmental peacebuilding be able to fully develop its potential to simultaneously address environmental problems and threats to peace.