Addressing the impact of humans on the environment is arguably one of the biggest challenges society faces, and large-scale ecological monitoring is needed to reliably assess the impact and establish relevant policies. However, such large-scale monitoring is often infeasible, primarily owing to resource limitations. Recently, organizations have started to use information technologies to enable public participation in such efforts. One major problem is how to motivate people to contribute and, more importantly, to encourage sustained participation. In this conceptual paper, we integrate research from crowdsourcing, human–computer interaction, and motivational affordances to propose design principles enhancing the intrinsic motivation of contributors to large-scale ecological monitoring projects. Specifically, drawing on research on crowdsourcing and motivational affordances, we argue that instantiating design principles addressing people’s needs for autonomy, competence, and relatedness can increase participants’ motivation and present recommendations for designers of systems supporting such projects.