A ground penetrating radar (GPR) survey was performed on the Egirdir Lake to obtain the structural properties of Kumdanli and surrounding faults. GPR data was collected along ten profiles in various directions by using 100-200MHz GPR antennas. The radar sections showed that the Kumdanli Fault, SW-NE in direction, and also some other neighboring NW-SE normal faults have played an active role in forming the Egirdir-Hoyran Lakes. The deformation and the geometry obtained from the results show that the Kumdanli Fault is a sinistral strike-slip fault including oblique and segmented displacements. The other faults (Kemerdami and Akkecili) have mainly normal fault systems. Their trends are generally NW-SE in direction. It is also observed that they are younger than the Kumdanli Fault system. These fault properties demonstrate the Egirdir Lake side has an extensional structure trending SW-NE.