In this work, hydrogeological study has been carried out in order to characterize thernaquifers and conceptualize the groundwater flow in Awassa Lake catchment, locatedrn275km south of Addis Ababa in the central sector of the Main Ethiopian Rift. Hydrometeorological,rnhydrological, geological, and structural, hydrochemical and isotopicrncharacteristics of the area are assessed through uses of various approaches andrnmethodologies. Fieldwork, observation and measurements of relevant variables along withrnexisting data accompanied by systematic analysis and interpretation helped so as tornunderstand the hydrogeological system.rnThe Awassa Lake catchment is a closed caldera Lake on its one segment overlaps with thernMain Ethiopian Rift. The main geological units in the area are lacustrine sedimentsrncharacterizing the floor; acidic volcanics covering the caldera rims and escarpment andrnsome basalts, hayaloclastites and scoria cones outcrop on the floor. As it is found on thernaxial zone of the Ethiopian Rift, it is highly affected by rift structures, recent tectonicrnfeatures are also observed in the area.rnThe aquifers in the area generally occur in unconfined condition where their hydraulicrncharacteristics are spatially highly variable, which is the result of the complex nature of thernlacustrine sediments and the degree of fracturing of the volcanic rocks. The most permeablernunit is the lacustrine sediment with hydraulic conductivity ranges between 5m/day-rn200m/day, where as the least are those acidic volcanics of the rhyolite, obsidian and lapillirntuff having less than 0.1m/day. The others volcanic rocks lie in between depending on therndegree of weathering, fracturing or faulting.rnThe hydrochemical and isotopic analysis of ï¤2H and ï¤18O result signifies that groundwaterrnof the floor, caldera rims, and escarpment and highland is found in different flow regime.rnThis is also supported by the large hydraulic gradient between the floor and the highland.rnGroundwater of the caldera rims, escarpment and highland is characterized by active,rnshallow flow with low EC less then 300Î¼s/cm and little isotopic fractionation. Intermediaternflow characterizes the remaining floor and western caldera rims with relatively higher ionicrnconcentrations (EC ranges between 1000-2400Î¼s/cm) and enriched in isotopic composition.rnThese flows are controlled by the rift faults and structures, which depends on therncharacteristics of these structures such as depth of penetration. The area gets higherrnamounts of direct recharge from the eastern and south eastern caldera rims, escarpment andrnhighland where as the other parts are characterized by intermediate and localized recharges.rnSimilar to the groundwater flow, discharge areas are also restricted to rift structures exceptrnthe swampy areas found on the floor. Not only these structures but also recent tectonicsrn(ground cracks) developed on the area control the groundwater flow. These featuresrnfacilitate the groundwater flow toward the Lake Awassa by increasing the hydraulicrnconnections of the different rock units, which might be associated with the rise of the Lakernlevel, the main problem of the area.rnKey words: Aquifer characterization, Awassa Lake catchment,conceptual profile model, groundrncracks, hydraulic conductivity.