Küçük Menderes (\"Little Meander\"), Cayster River, Caystrus River or Kaystros River (Ancient Greek: Κάϋστρος, romanized: Káÿstros) is a 114 km long river south of İzmir, Turkey. It generally flows westward and arrives at the Aegean Sea at Pamucak beach, near Selçuk, İzmir.
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.
