The construction of a hydroelectric dam involves the prolonged contest between pro‐ and anti‐dam coalitions adopting various storylines to provide the project with meaning. These representations of dams are often open to reinvention and transformation, allowing for the introduction of new portrayals. This work adopts Ernesto Laclau's and Chantal Mouffe's Discourse Analytic framework to explore how supporters of the Belo Monte project in Brazil have integrated narratives of environmental sustainability into the positioning of the facility. Following recent scholarship, these appeals to sustainability are cast as a tool to legitimize construction whilst concealing negative social and environmental consequences. In doing so, this work asserts that the ambiguity – or emptiness – of the concept of sustainability has allowed for the pro‐dam coalition to adopt such a storyline to legitimise a project that possesses questionable environmentalist credentials.