one sees a rapid process of rivers management modernization in brazil in the 90s - in legal and institutional terms. the approval of law 9,433/97 was one of the main reasons for the changes. it established the national system of hydrographic resources management based on decentralized and participative management principles. the hydrographic basin committees are one of the most important pieces of the new system. the effectiveness of their activities depends on the nature of the decision making process, specially its capacity of dealing with conjectural problems and local interests. this article aims to discuss the qualities and challenges of this process within the committees.