We conducted a field study (N = 1,579) to evaluate the impact of incentives on proenvironmental behavior, specifically with respect to waste sorting. To implement these incentives, we used a card-scanning technology that tracks biowaste sorting in real time. To interpret our findings, we introduced a theoretical model that formalizes prosocial decision-making in contexts where cheating can occur. The model reveals how the removal of incentives creates an opportunity to isolate the roles played by the extrinsic motivation to recycle or cheat in this context, thus making it possible to identify the effect of incentives on intrinsic motivation.On the basis of an evaluation of the effects of incentives over a long-time horizon, we observe that they initially increased recycling; however, this effect declined over time even when the incentives remained in place. Ultimately, the effect vanished after approximately 50 weeks. Crucially, we observe no discontinuity following the removal of incentives. In light of the theoretical model used in this research and several robustness checks, we interpret this pattern as evidence indicating that incentives did not influence extrinsic motivation -either to recycle or to cheat- but rather crowded in intrinsic motivation.