The Tone River, which originates from Mt. Ominakami in Gunma Prefecture, is the river with the largest basin area in Japan. It runs through four prefectures of the Kanto Plain and flows into the Pacific Ocean. While water demand in the Tokyo metropolitan area has increased sharply since the 1950s, droughts have occurred frequently, and as its flow rate has decreased accordingly, salt water has flowed backward to the river to about 50 km up from the estuary. This salt water intrusion has damaged field crops and at the same time caused unavailable water supply in large areas. Under these circumstances, the momentum for the construction of the estuary barrage increased in order to respond to drought, salt water damage as well as increasing water demand. As a result, at a point about 18 km upstream from the mouth of the Tone River, the construction of the main body of the Tonegawa Estuary Barrage started from November 1965, and was completed in 6 years. The management started in April 1971, and the 50th anniversary of the start of management was celebrated in April 2021.

During the past 50 years, the estuary barrage prevented salt damage in the basin area along the lower reaches of the Tone River and stabilized the water level on the upstream side and kept sending urban water to Tokyo, Chiba, Saitama prefectures, including Choshi City in Chiba Prefecture. And supplied irrigation water to the farmland in eastern part of Hokuso Region of Chiba Prefecture. During the fifty years, we experienced large earthquakes such as the 2011 Great East Japan Earthquake in Tohoku Region. Despite such earthquakes, the estuary barrage has kept playing its role without losing the functions. The estuary barrage will continue to play an important role in the river mouth in the next fifty years.