Arakawa River (Kantō) Arakawa River (Kantō) The is a long river that flows through Saitama Prefecture and Tokyo. It originates on Mount Kobushi in Saitama Prefecture, and empties into Tokyo Bay. It has a total catchment area of . The river is one of Tokyo's major sources of tap water, and together with the Tone River, accounts for around 80% of Tokyo's water supply. Attempts to control flooding of the Arakawa River have been made since the area that is now Tokyo became the de facto capital of Japan during the Edo period. Following a major flood in 1910 that damaged a large
Arakawa River (Fukushima) ineffective, and the river continued to periodically flood, culminating in a large-scale flood on August 5th, 1986. In 2004 the Arakawa River's flood control system was completely overhauled, and 13 new check dams were built along the main river and numerous other dams built on its tributaries. In 2008 the Agency for Cultural Affairs designated the Arakawa First Check Dam as a Registered Tangible Cultural Property. In 2007 the Arakawa River tied with six other rivers for having the best quality river water in country based on biochemical oxygen demand tests conducted by the Ministry of Land, Infrastructure, Transport and