Prior to the old River Act of 1896, flood control measures in Japan were executed on the principle of a co-existence of the river and human activity. Until the 19th century, through the feudalistic period, the public sector did not have plans for completely controlling a large-scale flood, as it is almost impossible by only technological methods, in particular, to control a major flood in monsoon Asia. In practice, people in monsoon Asia live away from river courses and lowlands in order to alleviate flood damage. Farmers in those areas planted crops that could withstand inundation. The flood control strategy of the public sector laid emphasis on protecting the castle or city centre area, but not defending the whole area where people were living. In areas not protected by the public sector, people formed their own groups to fight against flood damage. They were skilful at flood fighting, and were familiar with the characteristics of floods and the behaviour of inundation in their river basins. Thus a kind of public–private partnership existed at that time. Based on the River Act of 1896, the Japanese government began historical flood control measures, with the aim of completely controlling even a huge flood. They constructed a high, continuous levee system, with broadening river width, and dredging of the river beds in key rivers in Japan. Almost all river improvement works had been finished by about 1930. The flood damage in alluvial plains decreased remarkably as a result of these major works. However, after the Second World War Japan suffered from severe flood damage almost every year. During the period of so-called high economic growth, from 1950 to 1970, Japanese engineers overcame water shortage and flood damage by constructing many dams with various river improvement works. Because of the high level of engineering required, it became unnecessary to co-operate with the private sector. Due to the continuously active river works, the riparian environment and its ecosystems were destroyed everywhere. The private sector also played an important part in environmental protection. Environmental topics are different for each region and river, and therefore the public sector could not standardize plans for the whole of Japan. Here, the necessity of new partnerships between public and private sectors in the present flood control and environmental policy in Japan should be recognized. In reviewing these facts, the River Act was revised in 1997, by adding the terms “conservation of river environment” and “referring to the inhabitants' intentions”.