The line opened south of 145th Street just after midnight on November 23, 1904, as part of the IRT's original system. It was known as the East Side Subway or East Side Branch at the time, as it was the spur of the main line to the east side. The first train ran from the line onto the IRT White Plains Road Line (known as the West Farms Branch or the West Farms Extension) just after midnight on July 10, 1905. Soon after the line opened, it was speculated that it would bring prosperity to Harlem. The line ran across the path of the Harlem Creek, a creek that had once been located above ground but had been buried by the first decade of the 20th century. The creek's presence caused flooding in the line's early years, especially around 116th Street. In April 1907, IRT officials decided to create a concrete drain beneath the Lenox Avenue Line tunnel, during which time trains in both directions ran on the southbound track during late nights. In Fiscal Year 1910, the bottom of the tunnel at the south end of the 116th Street station was rebuild to prevent leaking.