The Metropolitan Area Outer Underground Discharge Channel is one of the world's largest underground discharge channels, which takes water overflow underground from small- to mid-size rivers to Edo River through a 6.3km long tunnel that runs 50m below ground. Construction was started in March 1993 utilizing world-class Japanese civil engineering technologies. After a construction period of 13 years, in June 2006 it became possible to direct water from the Oootoshifurutone River into the Edo River.