Purposeful collective action is important for sustainably managing many kinds of natural resource issues in social-ecological systems. However, cultivating purposeful collective action is challenging in ambiguous and contested situations involving multiple issues, actors, levels, and drivers, and weak or missing feedback. A particular example is the problem of managing waterway health in large and diverse landscapes. This paper analyses the emergence of purposeful collective action for managing waterway health, focusing on a case study of a large and diverse region in Australia. It applies a heuristic developed to guide inquiry into 'enabling capacities' underpinning purposeful collective action, to analyse three local cases embedded within a broader regional landscape. A diverse range of enabling capacities at both local and regional levels, and cross-level interplay between these levels, are shown to be important. Findings imply that efforts to generate purposeful collective action require building enabling capacities across multiple levels of organisation, from which contextually-appropriate and adaptive action can emerge. Moreover, findings indicate the need for a practice-focused 'knowledge-action perspective' that recognises the importance of intersubjectivity and agency. The paper demonstrates a promising approach for investigating purposeful collective action in ambiguous and contested water and environmental governance situations.