The Aksu (Bronze Age name in Hittite: 𒁉𒋻𒀀𒅀, Kaštaraya, ancient name in Greek Κέστρoς, Kestros), is a river in Antalya Province (southwestern Turkey), which rises in the mountains of Toros. The course of the Aksu is between the Düden to the west and of the Köprüçay to the east. It discharges into the Mediterranean near the city of Antalya. The river is about 145 km long and has a total catchment area of 3652 km². There are several lakes in its catchment area, including Lake Kovada and the reservoirs created by the Karacaören-1 and Karacaören-2 Dams.
The Aksu is primarily fed by karstic springs in the Taurus Mountains. In contrast to the many seasonal streams in the region, the Aksu flows year-round, although its volume can fluctuate dramatically throughout the year. Like other karstic streams, the Aksu does not carry much sediment with it.
