Abstract: The surface under investigation in the Fethiye plain is about450 km². The main geological formations are: various kinds of limestones, greenrocks, such as serpentine ,and alluviums. The main tectonic ,and morphologiccharacteristics are the numerous faults, karsts ,and flood cones. The yearly rainfall average is 1000 to 1200 mm, the temperature average is 19° ,and the yearlyevaporation average is 1200 mm. From the minimum yields of the small riversof the area, measured during the dry period, the minimum infiltration rate ofthe geological formations has been estimated ,and compared with similar resultsin other countries. From these conclusions we try to evaluate the undergroundwater reserves ,and losses of the Fethiye Plain.