The aim of this article is to analyze the dynamics that marked the coexistence between different actors in the environmental conflict caused by the salinization of surface and underground waters during the implantation of the Açu Port, in the municipality of São João da Barra, which is located in the Northern Fluminense region. The work seeks to demonstrate the links between this particular conflict and the profile of the major projects established to expand Brazil’s insertion in the world economy as an exporter of primary and semi-benefited products. From a methodological point of view, the work used a qualitative methodology based on a bibliographic and documentary survey related to the environmental impacts and conflicts caused by the Açu Port. The research results demonstrate the importance of having a transparent, participatory decision-making process guided by the sustainability of state actions in the planning and implementation of Large Investment Projects.