The Sea of Marmara links to the Black Sea via the Bosphorus Strait cutting through Istanbul, a city of 12 million people, and connects to the Aegean Sea through the Dardanelles Strait.
Crowded waterways
The two straits constitute the main naval route for Ukrainian and Russian vessels to reach the Atlantic via the Mediterranean and are listed among the most crowded waterways of the world.
Salih Reis-4, the Turkish ferry, returned to
Yenikapi on Istanbul's European side [AFP]
Tolga Uyar, a spokesman for the municipality-owned ferry company, said: "[The injured] are not in serious condition and are being transferred to local hospitals."

He said most of the injured passengers hit their heads on seats or other parts of the ferry during the collision.
Uyar said the accident occurred when the Turkish ferry - named Salih Reis-4 - rammed the anchored freighter - named Semyon Rudnev.
An investigation was launched to determine the cause of the accident in the Sea of Marmara, the Anatolia news agency said.
Ferry at fault
The maritime undersecretariat in Ankara said the passenger ferry had run into the cargo ship, which was anchored at the time.
In Kiev, the Ukrainian foreign ministry the Turkish ferry was at fault.
"According to initial information, the Turkish party is responsible for the accident," it said in a statement, adding that the ship's crew did not suffer any injuries.
Suffering only minor damage, Salih Reis-4 returned to Yenikapi. The Semyon Rudnev, which was waiting to take cargo from Istanbul to Ukraine, also suffered minor damage, Anatolia reported.