In order to use the energy and irrigation potential of the Euphrates River, a series of dams have been designed (upstream to downstream); Keban, Karakaya, Karababa (Ataturk), Birecik and Karkamis. The first three of these dams have been completed; construction on the Birecik and Karkamis dams is underway. The initial plans involved a 60 m high Golkoy dam, downstream of the Karakaya dam, with the Ataturk dam 60 m lower than it is currently. In the belief that the cost of irrigation by the Ataturk dam's water would be high, the increase of the height of Ataturk dam was preferred to the construction of the Golkoy dam. The Keban dam's basement is formed by karstic rock, named Keban marble. From the author and his colleagues' studies, it has been shown that water would leak from the left side of Keban dam reservoir, forming a spring in the Keban Creek. In order to prevent this water leakage, an intensive grouting programme was applied. In spite of this, when the reservoir was filled, 26-30 m(3)/s of water leaked from the Keban Creek. A more recent study on the volume of leakage showed it to be reduced to 7-8 m(3)/s, with this amount remaining constant. The Karakaya dam is constructed on metamorphic rocks thus only allowing minimal water leakage. However, on the downstream side of the right slope, the Tillo-Bego-Senketo landslides have been an important risk to the dam. If such landslides cause an artifical lake by blocking the Euphrates River, the Karakaya hydroelectric power station could be flooded. Limestone forms the foundations for the Ataturk dam. On and around the damsite, there is epithermal water (24-26 degrees C) below the aquifer, deeper than 300 m, with the level of the grouting curtain down to 180-200 m. The grouting curtain would not be able to prevent the leakage because the level of karstification extends below the grouting curtain. In February 1993, the total volume of leaking water from the damsite and its vicinity reached 10 m(3)/s when the reservoir level was 517 m. When the reservoir is full (542 m), the volume of leaking water is expected to increase. Under the clay core of the dam, extending from the surface to 30-40 m depth, high grouting pressure could not be applied, so water leaked at this part of the grouting curtain and thus the amount of leaked water could not be measured. (C) 1999 Elsevier Science B.V. All rights reserved.