Access to adequate quantity and quality of fresh water is critical to the well-being of Tanzania's human population, currently approaching 50 million. In the early 2000s, Tanzania revamped its legal and institutional frameworks related to freshwater resources management with the passage of the National Water Policy (NAWAPO) and the Water Resources Management (WRM) Act. Three major components of these frameworks are: the use of natural hydrological boundaries as units for management; the designation of an order for decision making on water allocation that prioritizes basic human and ecosystem water needs; and the encouragement of community participation in freshwater resources management. Institutionally, WRM now follows a nested approach, with the Tanzanian Ministry of Water operating at a national scale, nine basin water offices responsible for water allocation at a river basin scale, and formally recognized water users' associations as mechanisms for public participation at the catchment scale. To date, 93 water users' associations have been formed. Although some are active and appear effective, others are almost dormant, and not achieving their full potential as partners in WRM. In this paper, we provide context for the sweeping changes in WRM in Tanzania and review the lessons from more than a decade of implementation of the NAWAPO. We focus in particular on the role of the water users' associations, and use case studies of three basins - the Pangani, Wami/Ruvu, and Lake Victoria - to examine their strengths and challenges. Tanzania's experience offers lessons for other countries considering revision to legal and institutional frameworks around fresh water.