"Parha". Parha is likely the future Perga. The permanent supply of water, and the resulting fertility of the surrounding plain, was a contributing factor to the prosperity of the ancient city of Perga. As Kestros, the river is mentioned by Pomponius Mela as navigable, as far upriver as Perga, 60 stadia (about ) from its mouth, according to Strabo. It silted up over the Byzantine era, and Perga declined as a result. Today From the 1854 Dictionary of Greek and Roman Geography, the Aksu is " wide at its mouth, and deep within the bar, which extends across the mouth, and so shallow in places in its delta as to be impassable to boats that draw more than of water". The swell from the sea meeting the stream generally produces a violent surf." At its headwaters is the Kovada Lake and just below that the Karacaören Dam reservoir. Fauna A 2005 study found 17 different species of oligochaeta in various parts of the Aksu and its tributaries: Aulodrilus pluriseta, Aulodrilus pigueti, Potamothrix hammoniensis, Psammoryctides albicola, Tubifex tubifex, Limnodrilus ukedemianus, Chaetogaster diaphanus, Nais pardalis, Nais variabilis, Nais communis, Nais bretscheri, Dero digitata, Aulophorus furcatus, Pristinella osborni, Pristinella jenkinae, and Stylaria lacustris. Many of these species have a cosmopolitan distribution. Geology The Aksu Basin forms a sedimentary basin, part of the broader Antalya Basin, which has been infilling within the Isparta Angle formed by the intersection of the Aegean and Cyprian tectonic arcs since Neogene times. The Aksu Basin covers some 2000 square kilometers. On the west, it is bounded by the Bey Dağları platform carbonates. To the east, the Aksu Thrust separates it from the Köprü Çay Basin. The Aksu Basin overlies basement rocks of several types: Bey Dağları platform carbonates, Alanya Metamorphics, Antalya Nappes (made of ophiolite) and Lycian Nappes (platform carbonate). An unconformity separates the basin from these basement rocks. The Aksu Basin is considered a foreland basin. It can be divided into two sub-basins: in the north is the older Aksu-Karpuzçay sub-basin, and in the south is the younger Yenimahalle-Çalkaya sub-basin. There are five fan deltas in the Aksu Basin: Kapıkaya, Kozan, Karadağ, Kargı, and Bucak. There is also the Eskiköy alluvial fan. In front of the mouth of the Aksu River, there is a broad, shallow marine shelf offshore where the present-day sediments of the Aksu River are deposited. In the past, this area was deeper; according