This report presents the resource quality objectives (RQOs) and a reserve assessment for the Lower Mara River Basin (Lower MRB) of Tanzania. Activities reported are part of the project “Biodiversity Conservation and Sustainable Utilization of Ecosystem Services of Wetlands of Transboundary Relevance in the Nile Basin”, which seeks to build consensus and enhance cooperation in water resources management and development between the Nile Basin’s riparian countries. Results also contribute to the development of a water allocation plan for the Lower MRB under the Memorandum of Understanding signed by Tanzania and Kenya in 2015 for Joint Water Resources Management of the Transboundary Mara River Basin. The environmental Flow assessment report was developed and in close cooperation with and direct involvement of the Lake Victoria Basin Water Board (LVBWB) under of the Ministry of Water of Tanzania, which is the authority legally responsible for setting and protecting RQOs and the reserve in water resource management. The process involved Resource Quality Objective (RQO) setting through a stakeholder’s workshop, Environmental flow assessment and Reserve flow setting by specialists and water authorities. RQOs and the reserve are a requirement in Part VI (Protection of Water Resources) of the 2009 National Water Resources Management Act of Tanzania. RQOs are intended to protect water and related aquatic biological resources at levels needed to meet the needs of resource users and maintain ecosystems in a desired environmental management class