In 1966, the Yokkaichi and Suzuka water bodies were nominated a 'designated water bodies' under the Water Quality Control Law, andrestrictions were imposed on the oil content and other substances in factory wastewater being discharged into waters. In response to this, companies made efforts to improve the performance of oil separators and settling tanks.
The Water Pollution Control Law was passed in Japan in 1970. Prior to the implementation ofuniform regulations for factory wastewater, companies in Yokkaichi collaborated to treat wastewater and take other measures to meet the standards.