What is the longest river entirely within the country of Turkey?

The Kızılırmak, (Turkish for "Red River"), also known as the Halys River is the longest river entirely within Turkey. It is a source of hydroelectric power and is not used for navigation.

The Kızılırmak flows for a grand total of 1,355 kilometres (842mi), rising in Eastern Anatolia around 39.8°N 38.3°E, flowing first to the west and southwest until 38.7°N 34.8°E, then forming a wide arch, the "Halys bend", flowing first to the west, then to the northwest.

It then passes to the northeast of Lake Tuz, then to the north and northeast, where it is joined by its major tributary the Delice River.

The Delice river is at 40.47°N 34.14°E, it then zigzags to the northwest to the confluence with the Devrez River at 41.10°N 34.42°E, and back to the northeast, then joining the Gökırmak before finally flowing through its delta into the Black Sea at 41.72°N 35.95°E.

Dams on the river include the Boyabat, Altınkaya and Derbent.The Hittites called it the Maraššantiya. It formed the western boundary of Hatti, the core land of the Hittite empire.

The Kızılırmak, served as a natural political boundary in central Asia Minor, first between the kingdom of Lydia and the Persian Empire, and later between the Pontic Kingdom and the Kingdom of Cappadocia.

The river water is now used to grow rice and in some areas water buffalo are kept.