Source: All About Turkey
All but two of Turkey's rivers (the Asi and the Meriç) have their sources within its borders and there are seven river basins. The principal rivers in the Black Sea basin are the Sakarya, Kizilirmak Yesilirmak and Çoruh. There are also several rivers with short courses but high water flows in the Eastern Black Sea region, including the Ikizdere, Hursit Cayi and Firtina.
The Marmara basin has fewer rivers, the longest being the Kocaçay which rises on Mount Murat and flows into the Marmara Sea from the south.
In the Aegean basin are the Kücük Menderes, Büyük Menderes and Gediz rivers.
In the Mediterranean basin the main rivers are the Aksu, Köprüçay, Manavgat, Göksu, Ceyhan and Seyhan.
Only two major rivers flow from Turkey into the Caspian Sea, these being the Aras and Kura. Water from Turkey also flows into the Indian Ocean via the famous Euphrates and Tigris rivers.
There are two large inland drainage basins: the Central Anatolia basin in Konya, and the Yay, Seyfe, Kulu and several other less important satellite lakes.
The Karasu, Incesu, Deliçay and Bendimahi rivers flow into the interior drainage basin of Van.