Köycegiz is a town and district of Muğla Province in the Aegean region of Turkey.

The town of Köycegiz lies at the northern end of a lake of the same name (Köycegiz Lake) which is joined to the Mediterranean Sea by a natural channel called Dalyan Delta or simply as Dalyan. Its unique environment is being preserved as a nature and wildlife sanctuary, the Köyceğiz-Dalyan Special Environmental Protection Area. A road shaded with trees leads to the township that carries the same name as the delta, Dalyan, which is situated on the inland waterway, and which actually depends the neighboring district of Ortaca administratively. Dalyan is highly popular with visitors and its maze of channels is explored by boat. The restaurants which line the waterways specialize in fresh fish. High on the cliff face, at a bend in the river, above the ancient harbor city of Caunos, tombs were carved into the rocks. The Dalyan Delta, with a long, golden sandy beach at its mouth, is a nature conservation area and a refuge for rare loggerhead sea turtles (Caretta Caretta) and blue crabs.