Recreational fisheries are complex adaptive systems that are inherently difficult to manage due to a heterogeneous user group (consumptive vs. non-consumptive) that utilize patchily distributed resources on the landscape (lakes, rivers, coastlines). There is a need to identify which system components can effectively predict and be used to manage nonlinear and cross-scale dynamics within these systems. We examine how ecosystem size or waterbody size can be used to explain complicated and elusive angler-resource dynamics in recreational fisheries. Waterbody size determined angler behavior among 48 Nebraska, U.S.A. waterbodies during an 11-year study period. Angler behavior was often unique and nonlinear across waterbody sizes. For example, anglers spent more time fishing and harvested more fish at larger waterbodies compared to smaller waterbodies. Time fished increased across smaller waterbodies but reached a threshold at larger waterbodies. The number of fish released increased as a function of waterbody size across smaller waterbodies but then plateaued. Subtle changes in waterbody size caused abrupt changes in angler behavior—that is, waterbody size structures angler-resource dynamics in recreational fisheries. We believe that including waterbody size, a simple and easily measured metric, in fisheries management will increase effectiveness of cross-scale actions and minimize unintended consequences for recreational fisheries. Applying uniform management actions (e.g., harvest regulations) across small and large waterbodies may elicit contrasting angler-resource responses. Waterbody size may also be useful for understanding angler typologies. Based on our findings, we expect that ecosystem size is a prominent and valuable system component that will determine and explain coupled user-resource dynamics in other complex adaptive systems.