Ayase River

The Ayase River is a river in Japan.

Geography

The Ayase River, takes its source in the city of Okegawa in Saitama Prefecture then joins the Naka River in Katsushika, Tokyo. The latter flows into the river Arakawa River, before Tokyo Bay.

Development

The course of the river was developed in Edo period, when Edo became the shogunal capital of Japan. Historically, the first part of the river is used for irrigation and agriculture, the middle and the end for the supply of water to the population of Tokyo and for river transport.
The river caused several major floods.

Pollution

From the 1960s to the 1990s, the river was the most polluted in Japan, occupying twenty-five times the head of the classification of the most polluted rivers between 1972 and 2007. The pollution, which was caused by agricultural and industrial activities and the density of the population in close proximity to the riverbanks, led to cleanup projects in the late 1990s and during the 2000s.