Across the country, government agencies increasingly collaborate with non-governmental actors on environmental dilemmas to gain access to resources, expertise, and local knowledge; to mitigate conflict; and to share risks in a changing environmental context. Collec- tively, these often overlapping collaborations form a complex and dynamic governance network (GNet). This paper examines the establishment and growth of an envi- ronmental GNet over a period of 15 years in conflict-rid- den southeastern Arizona, USA. Using social network analysis, we detect the emergence of several influential organizations acting as political entrepreneurs and observe an overall change in network composition. We describe three phases: (1) a newly emerged network, (2) a network dominated by national non-governmental organizations, and finally (3) a shift toward local non-governmental organization involvement. Using institutional analysis, we explore how conflict over natural resource use, decreasing public and private monies for management, and increasing tensions over border security, leads to the establishment of new collaborations and new network participants. While this research focuses on environmental governance in southeastern Arizona, this methodological approach—and insights into the key role of organizations acting as political entrepreneurs—provides a useful starting place for ana- lyzing networks of collaborative governance in other geo- graphic and political contexts. Organizations' perceptions of risk and trust are keys to understanding the dynamics of collaboration within a GNet.