The construction of a large hydropower project in the Chilean Patagonia led to a debate which faced the arguments of developers and opponents. This article analyses the communication strategy of the main players in this emblematic controversy and outlines how both were adapted to the current situation, with varying degrees of flexibility, mobilising scientific-technical speech as a standing mark. However, as the conflict was mediated and positions were clearly defined, changes in the way the arguments were deployed were observed. While, in the case of opponents, there was a permanent involvement of scientists throughout the dispute, this was not the case with the sponsors. While these expert voices, who were recruited early by the company HidroAysén, were diluted during the conflict, it can be noted that their guments survived throughout the debate.