The social dimensions of river restoration are not well understood especially in the context of large-scale restoration projects embedded in a complex social-ecological system. This study used in-depth interviews with diverse stakeholders to examine perceptions of restoration success on the Clark Fork River Superfund project in Western Montana. Trust emerged as critical to restoration success and was influenced by public engagement, and by spatial and temporal scale. At this large scale, multiple relationships between agencies, NGOs, businesses, landowners, and other stakeholders meant that building trust was a complicated endeavor. The large spatial scale and long time frame made public engagement challenging, and landowners in particular were critical of the project, expressing mistrust in both agencies and the project as a whole. However, projects focused on smaller spatial scales, such as particular stream reaches, appeared to inspire more effective collaboration. Relationships between organizations were important at this large scale, but inter-organizational conflict affected trust across the project. Further, because trust requires accepting vulnerability, recognizing the differential vulnerability that particular groups and communities experience, based on the risks and benefits they accrue relative to the project, is important.