Collaborative partnerships around the world address environmental challenges from a local perspective. At the same time, many of these efforts are based on scientific information. Local and scientific information are not always compatible, and numerous challenges arise at the science-policy interface in collaboration. This study identifies key factors affecting the science-policy interface, including credibility, salience, legitimacy, and communication, as well as two-way interactions and compatibility with local knowledge that are important in collaborative governance. The importance of these factors is illustrated in a case of collaborative watershed management in the Canterbury Region of Aotearoa New Zealand. The case tells the story of local community members’ contestation of science used by the government to determine the health risks of recreational swimming and the role of collaboration in bridging experiential and scientific knowledge. Evidence from meeting observations, documents, and interviews indicates points of contention and how the collaborative forum successfully served as a boundary spanner to navigate the science-policy interface.