The Sakarya (Turkish: Sakarya Irmağı) is the third longest river in Turkey. It runs through what in ancient times was known as Phrygia.The source of the river is the Bayat Yaylası (Bayat Plateau) which is located to the northeast of Afyon. Joined by the Porsuk Çayı (Porsuk Creek) close by the town of Polatlı, the river runs through the Adapazarı Ovası (Adapazarı Plains) before reaching the Black Sea.