A thorough understanding of lakes hydrology is crucial before any usage of the lakes forrndifferent development works. In Ziway-Shalla basin where there is complex inlcractionrnbetween the lakes and groundwater system, stable isotope water balance method isrnemployed in this work to estimate the grou ndwater exchange rate for the geographica llyrnclustered lakes of the basin.rnAlthough the stable isotope water balance method has limitation due to lack ofrnmeasurement of environmental parameters, the existence of tenninal lake, Lake Abiyatarnin the basin gives a chance to estimate these environmental parameters that are importantrnin groundwater quanti fi cat ion. These environmental parameters would have been difficu ltrnto measure. The unknown 5A, isotopic composition of the atmospheric moisture forrnZi'jÂ»'1y - Shalla basin is estimated to be -16.8%0 and the limiting isotopic composition (5â€¢)rndetermined to be 12.5 %0. The lakes are evaporated with respect to the present dayrnprecipitation and the surface and ground waters between the lakes are influenced by thernlakes indicating the hydraulic link between surface and groundwater.rnThe result of stable isotope water balance shows that the lakes are influenced by differentrndegree of groundwater fl ux .The groundwater inflow to lake La ngano and Shalla isrnsignifi cant while the inflow to lake Abiyata is minimum. The groundwater outflow fromrnLake Ziway is signifi cant which may become groundwater inflows to the tworndownstream lakes, Abiyata and Langano. Lake Langano is characterized by modestrngroundwater outflow next to the two terminal lakes in the basin.