The Dardanelles is a narrow strait in northwestern Turkey connecting the Sea of Marmara with the Aegean Sea. It is one of two extremely important Turkish Straits, along with its counterpart, the Bosporus. The strait is 61 kilometers (38 mi) long but only 1.2 to 6 kilometers (0.75 to 3.73 mi) wide, averaging 55 meters (180 ft.) deep. The current flows in both directions along the waterway, from the Sea of Marmara to the Aegean via a surface current and in the opposite direction via an undercurrent. This passageway separates Europe (the Gallipoli peninsula) from the mainland of Asia (Anatolia). The strait is an international waterway, and together with the Bosporus, the Dardanelles connects the Black Sea to the Mediterranean Sea.