This paper maps the web presence of environmental nonprofit organizations (ENPOs) in Canada. It focuses upon a sample of 43 websites which were examined in April/May 2009. All of the websites belong to member organizations of the Climate Action Network-Canada, a peak ENPO with collaborative networks in the United States and Europe. Our interest is in examining the extent to which the online activities of ENPOs correspond with a ‘broadcast’ paradigm—based on the principle of one-way information flow—or a two-way ‘dialogical’ paradigm of communication. Special attention is given to addressing the use of social media technologies (Web 2.0) by these ENPOs, including Facebook, Twitter, RSS feeds and blogs. The findings interrogate the tension between instrumental and dialogical forms of communication. They also demonstrate that although there are cases of effective web-based communication by ENPOs, most are not leveraging the potential these technologies afford for constituency engagement, relationship building and conversation. The findings contribute to scholarship on nonprofit communication, environmental communication, social media and public relations.