Turkish rescue teams on Tuesday were searching for the third day in the Bosphorus for a missing Russian swimmer.
Authorities said 30-year-old Nikolai Svetschnikov took part in Sunday's annual Bosphorus Cross Continental Swim but never reached the finish.
Coast guard vessels have combed the strait without finding any trace of him, and an investigation has been launched, according to Istanbul governor's office.
His wife told the Russian channel Shot that she spent the night searching the shoreline, while relatives and friends also organized their own efforts.
The couple has an 8-month-old son. Another Russian participant said he had overtaken Svetschnikov early in the race, describing him as swimming slowly in breaststroke and stopping frequently.
The 6.5-kilometer race, in which swimmers cross from Asia to Europe, drew 2,800 athletes from 81 countries this year.
The Bosphorus, which is closed to ship traffic during the event, is known for its strong currents and challenging conditions.
