This article examines watershed cumulative effects assessment and management (CEAM) in the Athabasca watershed, Alberta, Canada. Using a focus group and semi‐structured interviews with 30 key informants from government, industry, NGOs, and First Nations, watershed CEAM was examined based on eight requisites to support CEAM: the presence of a lead agency; enabling legislation; financial and human resources; data management and coordination; multi‐scaled monitoring; CEAM baselines, indicators, and thresholds; multi‐stakeholder collaboration; and vertical and horizontal linkages. Results show that while there was broad agreement amongst participants concerning the necessity for these requisites, there was also considerable uncertainty respecting these requisite performances in this watershed. Several contributing factors may help explain this uncertainty. Participants noted a lack of willingness to share data to support CEAM, especially spatial data, as well as a lack of confidence in the integrity of water monitoring data. An absence of coordination and leadership for watershed CEAM has contributed to financial, human, and technical capacity limitations as well as power asymmetries respecting multi‐stakeholder engagement. Our results suggest that notwithstanding investment in cumulative effects science and monitoring in the Athabasca, advancing watershed CEAM requires much greater attention to the institutional requisites to implement and sustain CEAM programs.