This article presents research results about the ecoterritorial impacts from the construction of the “El Cajon” Hydroelectric Dam in the State of Nayarit, Mexico. The study confirms existing evidence demonstrating that the construction of hydroelectric megaprojects often brings about ecological decline, patrimonial losses and ecoterritorial conflicts. In the case studied the transformation of the river flow into a dam reservoir allowed the development of a productive fishery enclave, but the process changed the ecological functions of the water body. Moreover, the reservoir became an attractor for the arrival of actors external to the community, who had links with organized criminal gangs and monopolized the control of the regional thorough the use of systematic violence against the population. The paper discusses the strategies of resistance adopted by the population, which was composed mainly by members of the Wixarika ethnic group, against the unleashing system of crime, dispossession and violence and the resulting territorial reconfiguration. This process was grounded on the implementation of a form of “clandestine governance”, which favoured the advance and consolidation of a new and highly violent expropriatory regime, which had negative results for the region’s ecological systems and the living conditions of the communities.