Bosphorus is a straight that divides the city into 2: as Asia & Europe continents. It is 32 km long, and the Sea of Marmara flows over Bosphorus towards the Black Sea at a rate of sometimes 5-6 km per hour. That’s why it looks like a river. There is also a counter current at deep levels of Bosphorus from the Black Sea towards the Sea of Marmara. Therefore, waters of Bosphorus are always changing.
Narrowist point of Bosphorus is around 700 m, at the point where the Rumeli Fortress was built by Fatih Sultan Mehmet, 1 year before he conquered Istanbul. The widest point is around 3,5 km at the mouth of Black Sea over Sariyer.
Bosphorus shores used to be full of fisherman’s villages. The names still call out for villages, the shores of Bosphorus today are beautiful, very popular and very expensive to live. The villas (Yali in Turkish) along the shores of Bosphorus are today among most expensive houses in the world, with 10-15 million USD prices to own.
Bosphorus is an international water passage according to Montreux Agreement of 1936. That means international commercial and non-commercial ships can pass through Bosphorus freely: they only need to get Turkish guide captain to help them pass through this difficult water passage. Sometimes large ships collide with one-another, or sometimes they run aground crashing into the expensive villas of Bosphorus.
Today, one can enjoy the daily boat cruises over the Bosphorus, which take around 2 hours for full tour. There are shorter cruises. One of the most beautiful experiences in Istanbul is to have a dinner-cruise over the Bosphorus with shining view of Villas, Palaces, and beautiful shores of Bosphorus.