Shipping accidents are a threat to the maritime environment and to human life in the highly populated areas around the straits.
The Bosphorus is a narrow "S-shaped" channel of complex nature with several sharp turns and headlands, which prevent a proper look-out, and with changing currents.
The density of maritime traffic in the Bosphorus, which links the Black Sea to the Marmara Sea, has increased elevenfold from around 4,400 ships passing annually in 1936, when the Montreux Convention was signed to regulate transit and navigation in the Straits, to an average of 48,000 vessels per year recently.
[clarification needed] With 132 vessel transits daily, not including local traffic, it ranks second to the Malacca Straits in density.
During the period from 1953 to 2002, 461 maritime incidents occurred in the Istanbul Strait or in its southern entrance at the Marmara Sea.