The Kızılırmak, once known as the Halys River and Alis River, is the longest river flowing entirely within Turkey. It is a source of hydroelectric power and is not used for navigation.

The Kızılırmak Delta is the delta of the Kızılırmak River where it flows into the Black Sea, 40 km east of the city of Samsun. The delta is the third largest in Turkey and has the biggest wetland in Turkey's Black Sea Region. The wetland is a key biodiversity area and one of several internationally important Ramsar sites in Turkey because of its rich bird and plant life. There is a bird reserve which is important for migration.