The Bishan tunnel flooding was a major incident on the North South MRT line (NSL) of the Singapore MRT which occurred at 5.33 pm on 7 October 2017. The flooding of the tunnels between the Bishan and Braddell MRT stations was caused by heavy rain and a faulty maintenance pump. The flooding of the tunnels made the passage impassable, and bridging bus services had to be deployed while the Singapore Civil Defence Force and maintenance staff removed the water from the tunnel. The incident caused more than S$2 million in damages and lost revenue for the operator SMRT and led to the firing of eight maintenance employees.