荒川 (関東) The Arakawa River Japan *virtual tour.

The Arakawa River is a 173-kilometre (107 mi) long river that flows through Saitama Prefecture and Tokyo. Its average flow in 2002 was 30m³/s.
It originates on Mount Kobushi in Saitama Prefecture, and empties into Tokyo Bay. It has a total catchment area of 2,940 km2 (1,140 sq mi).
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 as of 2018. The Okubo water purification plant takes water from the river.
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 part of central Tokyo, a 22-kilometre (14 mi) long drainage canal was constructed between 1911 and 1924. In 1996 an agreement was signed to make it a “sister river” of the Potomac River in the eastern United States. This means that officials and volunteers from both river areas collaborate with each other.

荒川（あらかわ）は、埼玉県および東京都を流れ東京湾に注ぐ河川である。一級水系である荒川水系の本流で一級河川に指定されている。水系として、流路延長173 km、流域面積2,940 km2。川幅（両岸の堤防間の距離）は御成橋（埼玉県鴻巣市・吉見町）付近で2,537 mになり、日本最大である。江戸時代に行われた河川改修である荒川西遷事業により流れを変えられた歴史を持つ。