| Cayster River | |
| Subdivision Type1: | Country |
| Length: | 1140NaN0 |
| Source1 Elevation: | 2200NaN0 |
| Mouth Elevation: | 0m (00feet) |
| Discharge1 Avg: | 11.45m3/s |
| Basin Size: | 35020NaN0 |
Küçük Menderes ("Little Meander"), Cayster River, Caystrus River or Kaystros River (Greek, Ancient (to 1453);: Κάϋστρος|Káÿstros) is a river south of İzmir, Turkey. It generally flows westward and arrives at the Aegean Sea at Pamucak beach, near Selçuk, İzmir.
The ancient city of Ephesus was once an important port on the river,[1] but over the centuries, sedimentation gradually filled in the inlet around the city. The ancient port of Panormus was near its mouth.[2] The coastlines moved seaward, and the ruins of Ephesus are now some 8km (05miles) inland from the coast.
Its tributaries are the Fertek, Uladı, Ilıca, Değirmen, Aktaş, Rahmanlar, Prinçci, Yuvalı, Ceriközkayası, Eğridere, Birgi, Çevlik and Keles.
The river is currently just north of the Büyük Menderes ("Great Meander") River; both rivers have often changed their course.