Bosphorus is the name of the strait which lies between Europe and Asia. The strait Bosphorus connects the Sea of Marmara to the Black Sea and its length is approximately 30 km., 21 mile long. It runs in the general direction of NE to SW and varying greatly in width from 700 m. 0.45 mile to over 3500m. 2 miles at its widest. Its depth is generally 50-75 m., 150-200 feet but at some points reach to 100 m. 300 feet. There are two strong currents in the sea, one is from the Black Sea towards the Sea of Marmara which runs from the surface due to the low salt density and level difference of two seas. The other current lies from the reverse side, from the deep, towards the Black Sea. Because of the dangerous currents and the narrowness of the strait, all the ships passing through the strait should have pilots.