The fourth of the 1387 meter long tube tunnels within Marmaray project, which will combine the two sides of Istanbul was sunk to a depth of 48.5 meters yesterday. And the length of the immersed tubes reached 540 meters. All of the tunnel tubes will be immersed until the end of 2008in the project in which a total of 11 tubes will be immersed to the sea floor. The whole Marmaray project will be completed at the end of year 2010.