Even though collaborative governance has become an important model to address river problems, the practice of collaboration among different sectors to govern river problems is weak in Addis Ababa city. Therefore, this study was intended to investigate the problem of weak cross-sectoral collaboration for the governance of river problems in Addis Ababa City. Employing qualitative research approach, the study relied on both primary and secondary data sources. Accordingly, interview and observation were conducted to gather relevant data. Secondary data were collected from different quarterly reports, river assessments and researches. The study found out that cross-sectoral collaboration is characterized by the lack of involvement of various non-governmental sectors, the problem of legitimacy, and the representation of sectors by individuals who have no expertise or experience on river issues. On the other hand, the challenges are the exclusion of river from the agendas of each sector, lack of commitment of authorities to share information and resources, and the absence of sectors in the implementation of river plans in different river sites in terms of giving trainings, supervising, and evaluating river sites. Establishing committee at all levels, including river in the annual plans of each sector, and appointing river experts in different sectors are identified as important mechanisms of dealing with collaboration problems. These problems of weak cross-sectoral collaborative governance of rivers had resulted in the deteriorating quality of rivers, environmental hazards to the vegetation of agricultural crops, and health and related impacts on biotic elements of the ecosystem.