The Water Evaluation and Planning (WEAP) system model of the Mara River Basin was developed as a collaborative effort between IHE Delft Institute for Water Education (IHE) and the Stockholm Environment Institute (SEI). The historical and baseline conditions are representative of the researchers’ best understanding of the basin as it has existed and been used historically, as it exists and is used today, and how it will exist and be used into the future, without any major changes.