Erdek Gulf is a gulf of Marmara Sea, Turkey. It is administratively a part of Balñkesir Province. In fact, the gulf is named after Erdek, an ilçe (district) of the Balñkesir Province which is situated at the north coast of the gulf . The midpoint of the gulf is at about . KapñdaàPeninsula, Paà Âalimanñ Island and Avà Âa Island are to the north, Belkñs Tombolo (connecting KapñdaàPeninsula to the Anatolia mainland) is to the east, Karabiga ilçe is to the west and the Marmara coast of Anatolia is to the south. The maximum depth of the gulf is .
There are ferry services in the gulf. One service is to Barbaros in the Thracen side of Turkey, close to TekirdaÃÂ. There are also ferry services to the nearby islands such as Marmara Island (Saraylar terminal), Avà Âa Island and the Paà Âalimanñ Island.