The Kozakli-NevAYehir geothermal field extends a long a NW-SE direction at SE of the Centrum of Kozakli. The area is not rugged and average elevation is 1,000 m. The Kozanozu Creek flows towards north of the area. In the Kozakli thermal Spa area, thermal waters are manifested along a valley with a length of 1.5 km and 200 m width. In this resort some hot waters are discharged with no use. The thermal water used in the area comes from wells drilled by MTA. In addition, these waters from wells are also utilized by hotels, baths and motels belonging to City Private Management, Municipality and private sector. The measured temperature of Kozakli waters ranges from 43-51A degrees C in springs and 80-96A degrees C in wells. Waters are issued in a wide swampy area as a small group of springs through buried faults. Electrical conductivity values of thermal spring and well waters are 1,650-3,595 mu S/cm and pH values are 6.72-7.36. Kozakli cold water has an electrical conductivity value of 450 mu S/cm and pH of 7.56. All thermal waters are dominated by Na+ and Cl-SO4 while cold waters are dominated by Ca+2 and HCO3 (-). The aim of this study was to investigate the environmental problems around the Kozakli geothermal field and explain the mechanisms of karstic depression which was formed by uncontrolled use of thermal waters in this area and bring up its possible environmental threats. At the Kozakli geothermal field a sinkhole with 30 m diameter and 15 m depth occurred in January, 17th 2007 at the recreation area located 20 m west of the geothermal well which belongs to the government of NevAYehir province. The management of the geothermal wells should be controlled by a single official institution in order to avoid the creation of such karstic structures affecting the environment at the source area.