Globalization increases the vulnerability of traditional socialecological systems (SES) to the incursion of new resource appropriators, i.e. intruders. New external disturbances that increase the physical and sociopolitical accessibility of SES (e.g. construction of a new road) and weak points Resource intruders and robustness of social-ecological systems 411 in institutional SES of valuable common-pool resources are some of the main factors that enhance the encroachment of intruders. The irrigation system of the northwest Murcia Region (Spain) is an example used in this article of the changes in the structure and robustness of a traditional SES as a result of intruders. In this case study, farmers have traditionally used water from springs to irrigate their lands but, in recent decades, large agrarian companies have settled in this region, using groundwater to irrigate new lands. This intrusion had caused the levels of this resource to drop sharply. In an attempt to adapt, local communities are intensifying the use of resources and are constructing new physical infrastructures; consequently, new vulnerabilities are emerging. This situation seems to be heading toward the inevitably collapse of this traditional SES. From an institutional viewpoint, some recommendations are offered to enhance the robustness of SES in order to mitigate the consequences of intruders.Keywords: Adaptability, common-pool resources, globalization, groundwater, institutions, resilience, water management Acknowledgments: We would like to thank the Irrigation Communities for sharing their knowledge and experiences with us on springs, groundwater, agriculture and institutions. This research was funded by the Fundación Instituto Euromediterráneo del Agua (Murcia, Spain). Irene Pérez was supported by Fundación Séneca (Murcia, Spain) under a postdoctoral fellowship and Alicia Tenza by Generalitat Valenciana under a predoctoral fellowship. We would like to thank Juan de Dios Cabezas and David Martínez for data providing on springs flow. We are grateful to three anonymous reviewers for their constructive comments and suggestions.