Aksu Deresi rises in Karagöl, a rural highland area located very near to provincial borders of Giresun, Ordu and Sivas provinces. Karagöl is a chain of mountains which is part of the Giresun mountains, in the south of Dereli district of Giresun, and its summit is 3107 meters high. There is a crater lake on its summit, at 3,107 metres (10,194 ft) above sea level. The Aksu creek flows down to the Black Sea passing Kızıltaş, Sarıyakup, Pınarlar [tr] and Güdül villages. Its mouth is next to the eastern part of Giresun city. The Aksu Deresi is 60 kilometres (37 mi) long.