Heavy fog has halted sea traffic in Istanbul's Bosporus Strait on Monday, with some ferry services being cancelled.Istanbul Şehir Hatları ("Istanbul City Lines") announced early in the morning that it cancelled all of its services, except the Haliç (Golden Horn) line, but later on in the day it said that line was also cancelled.The fog has not affected the air traffic.Every day thousands of people in Istanbul take a ride on ferries to cross the Bosporus strait from the Asian to the European side and vice-versa.Istanbul's Bosphorus Strait is one of the busiest sea routes in the region.