From its source of Mount Murat in Kütahya Province, it flows generally west for 401 km (249 mi) to the Gediz River Delta in the Gulf of İzmir.

The Gediz is one of the two candidates for the Hittite placename Seha River, the other being the Bakırçay.

The Gediz Delta is important as a nature reserve and is home to rare bird species.

[3] However, the reserve suffers from water shortages due to heavy demands from irrigation projects, connected to the Demirköprü Dam.

These factors contributed to the river's formerly rich fish reserves to become a thing of the past in recent years.