The Study was conducted in Ziway-Abiyata Catchment in the Central Rift Valley of Ethiopia,rnto assess the effects of current and future water use practices on the hydrology mainly lakernlevel change of the Lake Abiyata and its surroundings using a WEAP model. Records ofrnhydrology, meteorology, irrigation, domestic water supply and industrial water supply forrnthe study area have been statistically tested and arranged as an input data source to fit thernmodel. Hydrologic and climatic data were correlated with lake levels. The demand and thernsupply of water resource, base line data and the future development activities of the arearnwere compared using mainly three different scenarios SN1, SN2 and SN3. While by alteringrnthe priority settled for the Bulbula River s flow to a least priority level, additional threernscenarios SN11, SN22 and SN33 were generated. The results revealed that unless thernminimum historical flow requirements are maintained, all scenarios indicated the futurerneffects on Lake Abiyata. For the SN1, the lake level declined by 0.79 m and 0.34 m for Ziwayrnand Abiyata lakes respectively. While compared with the baseline scenario, in the SN11 thernlake level drops were 2.61 m and 0.59 m for Abiyata and Ziway lakes respectively. The SN2rnscenario revealed a decline by 0.89 m and 0.42 m for the Lake Ziway and Lake Abiyatarncompared with the baseline scenario respectively. But in the SN22 scenario, a maximumrnlevel drop over the simulation period of 3.5 m and 0.7 m below the mean value of thernexisting condition for Lake Abiyata and Lake Ziway respectively was predicted. The SN3rnoption had less level drop effect compared with the SN2 scenario for both lakes despite thernadditional level drop by this development. The lake level drop below the natural sill in LakernZiway may result in the total dry up of the Bulbula River, which consequently threatens LakernAbiyata s existence as a permanent lake. Similarly, compared with the lake baseline meanrnlake level, the Abiyata Soda Ash Enterprise expansion will drop the Abiyata Lake level byrnabout 0.09 m, which was less than the effect due to upstream irrigation developmentrnproposition in a general sense. It is necessary that more detailed resource assessment ofrnwater should be done, including sustainable abstractions (safe yields) and the spatialrnvariability of water quantity. In addition to this, the new projects on the study area demandrnIntegrated Water Resources Management and Environmental Impact Assessment before thernrealization of the projects.rnKey words: Central Rift Valley Lakes, WEAP model, Lake Abiyata, lake level change.rnDescriptions of scenarios