Ecosystems have been stabilized by human interventions to optimize delivery of certain ecosystem services, while at the same time awareness has grown that these systems are inherently dynamic rather than steady state. Applied research fields have emerged that try to increase adaptive capacity in these ecosystems, using concepts deriving from the theory of complex adaptive systems. How are these concepts of complexity interpreted and applied by practitioners? This study applies a mixed-methods approach to analyze the case of freshwater management in The Netherlands, where a management paradigm promoting nature-fixating interventions is recently being replaced with a new paradigm of nature-based solutions. We find that practitioners have widely varying interpretations of concepts and of how the ecosystems they work in have evolved over time when described with complex system attributes. This study allows for the emergence of key complexity-related considerations among practitioners that are not often discussed in literature: (i) the need for physical and institutional space for self-organization of nature; (ii) the importance of dependency and demand management; and (iii) trade-offs between robustness and flexibility. This study, furthermore, stresses the importance of using practitioners’ views to guide applied research and practice in this field.