The Ruvu Environmental Flow Assessment (EFA) was an interdisciplinary effort to develop a first set of environmental flow recommendations for rivers of the Ruvu Basin, Tanzania. EFAs have become a common and scientifically accepted method for determining the quantity, quality, and timing of flows needed to sustain freshwater ecosystems and ecosystem services. EFAs recognize that rivers have natural periods of both high and low flows, and that these variations play important roles in river ecosystem functioning and thus should be protected as components of the reserve. In Tanzania, national water policies and laws call for the protection of the reserve or environmental flows in all aquatic ecosystems. In fact, freshwater needs for ecosystems are accorded second priority in decision-making about water allocations in Tanzania, following basic domestic uses of water. Toward this end, the Ruvu EFA aimed to fill an important gap in scientific information for management of water resources in the basin. This effort was conducted by a diverse team, which included the Tanzanian Ministry of Water, the Wami/Ruvu Basin Water Office (WRBWO), and Tanzanian and international scientists (hydrologist, hydraulic engineer, aquatic ecologist, fluvial geomorphologist, and riparian specialist).