This paper examines the drivers of cooperation among organizations dealing with common-pool resource (CPR) problems, particularly in transboundary water quality management in the Rhine catchment area. It explores the impact of threat perception and exposure on collective action and highlights the significant role of forums in enhancing cooperation. Using survey data and advanced network statistics (exponential random graph models), the study finds that while problem exposure influences cooperation, participation in forums has a more substantial impact on fostering joint action.