Drawing on fieldwork (interviews and web site content analysis) realized in Belgium and in Canada about two contrasted environmental controversies, this paper analyzes the different ways environmental activists exploit digital technologies and interact with journalists and communication professionals in order to build their image in the public sphere so as to gain and to keep access to the public sphere. Our theoretical frame combines insights from social movements (Gamson 1991, Polletta and Jasper 2001, Treré 2012) and digital communication studies (Broustau 2014, Yates 2015) in order to investigate the link between communication strategies in the digital era and processes of identity construction among social movements. This frame led us to build analytical tools, an interviews grid and a grid of Web content analysis, in order to study two cases: the nuclear phasing-out controversies in Belgium (from 2013 to 2019) and the controversies surrounding the Energie-Est pipeline project in Canada (from 2014 to 2018). Interviews with activists, journalists and communication professionals in the environmental field were confronted with the analysis of the websites and social medias of environmental activists and institutions. The results of this comparative empirical work point out the dilemma of anti-system communication strategies versus the search for media legitimacy and authority. We discuss these results in light of the controversies that oppose social movement experts (Harlow 2012, Diani 2013) and media sociologists (Gerbaudo and Treré 2015) stating that the use of social network tools by social movement organizations (SMO) transform the very nature of social movements.