Abstract:The paper contributes to the social-ecological systems literature by adapting and using Elinor Ostrom's Social-Ecological System (SES) framework in the context of a coastal ecosystem. We modified the SES framework in the case of the Ciénaga Grande de Santa Marta (CGSM), an estuarine lagoon in the Caribbean coast of Colombia. The ecological importance of CGSM and its species is undeniable. This paper aims to understand why collective action for a sustainable use of CGSM's fishery resources has not taken place. In order to respond to that question, we created new variables within the social, economic, and political settings of the SES framework. The results show that the fishers' fear of the indiscriminate and strong violence that illegal armed groups have inflicted on them since the 1960s and the economic development in the Colombian Caribbean region help explain the lack of collective action.Keywords: Ciénaga Grande de Santa Marta, collective action, Colombia, common-pool resources, conflict, fisheries, Social-Ecological System (SES) framework Collective action in a tropical estuarine lagoon 335 Acknowledgement: We thank INVEMAR's researchers, especially Efraín Viloria and Myriam Vargas for providing outstanding support for this research. Special thanks to Micaela Kulesz for her support and discussion in the early stages of this paper. We appreciate very much comments from Ana Maria Roldan on an early version of this manuscript. We are very thankful to CGSM's fishermen, in particular fishermen from Tasajera, because without their help this research would not have been possible. We would like also to express our gratitude to INVEMAR's field assistants in CGSM, in particular to Vladimir Carbonó for his valuable and constant support. Likewise, we want to thank Rubén Vásquez and Alexander Acuña for all their assistance in the field when we conducted the survey. We also appreciate comments received in an early version of this paper from participants in the WOW5 Conference at Indiana University. We value the editing work done by Joanna Broderick. Finally, we would like to thank two anonymous reviewers who have contributed valuable comments. This research was funded and supported by the Leibniz Center for Tropical Marine Ecology (ZMT) and the German-Colombian Center of Excellence in Marine Sciences (CEMarin).