Good governance is emerging as an approach to complex, transboundary and multi-party environmental challenges. Collaborative management is considered a form of good environmental governance as it addresses such challenges through pluralistic decision-making and actions. This research study explores and analyzes the process of collaborative management. This is done through an investigation of two river-based nonprofit organizations: the St. Croix International Waterway Commission and the St. John River Society. The research specifically investigates the evolution of the organizations, experiences of participants involved in the collaborative process, and factors which influence this process.A multiple case study research design was employed to conduct this study. Document analysis, observations and interviews were used to collect data for each case site over the course of a three month field season. Qualitative data analysis for each organization occurred through open and axial coding. A cross case analysis was then used to compare patterns and themes for each case.Despite forming in different ways, results indicate that the organizations have evolved to a similar state of operation, exhibit similar characteristics of collaborative management (transactive decision making, social learning and shared action/commitment), and show similar influences on collaboration. These influences, or drivers, were: formal legislated agreements; real or imagined crises; leadership; social networks and resources. These findings contribute to the collaborative management literature, and enhance understanding of what drives the collaborative process. Implications for river management, policy development and future research directions are offered.