In response to the report by the second Research Committee of the Mining Pollution, Watarase Yusuichi (Watarase Pond), the control basin for settling mineral poison was built on the prefectural borders between Tochigi, Gunma, Saitama, and Ibaraki Prefectures.
第二次鉱毒調査会の報告書を受け、栃木県、群馬県、埼玉県、茨城県の境に、鉱毒沈殿用の渡良瀬遊水地が作られた。