Köyceğiz is a long, brackish lake about 8km north of Dalyan, fed by mountain streams from the Toros range and drained southward through the river channels that pass the town. The lake covers around 50 square kilometres and is part of the Köyceğiz-Dalyan Specially Protected Area, which also covers Iztuzu Beach.
You can reach it by boat from Dalyan or by road from the town of Köyceğiz on the northern shore. The water is calm and warm in summer, and there are quiet swimming spots away from the resort jetties. Birdwatchers come for herons, kingfishers, and (in winter) flamingos along the reed margins.