Tsuda was the pioneer of freshwater biomonitoring using macroinvertebrates in Japan, having imported the techniques from Germany in the late 1950s. He compiled the first comprehensive keys to aquatic insects (Tsuda 1962), which also included an introduction to Saprobien System and Beck's Biotic Index. His books and systems have been widely used by both biologists and sanitation engineers for more than 20 years. After that time, a number of indices were tested as means of measuring organic pollution and ecosystem health of Japanese rivers. Recently, BMWP Scores based on groups of benthic macroinvertebrates were also adopted. In 1984, the Ministry of the Environment started a nationwide biomonitoring program for organic pollution using aquatic organisms. The Ministry of Land, Infrastructure, and Transportation of Japan also cooperates with this program. More than 800 000 professionals, amateurs, and private citizens join the program every year. The latter ministry and regional governments conduct a program, National Censuses on River Environments, to collect basic information on riverine habitats and organisms. The census, which covers 109 rivers and major reservoirs, inventories macroinvertebrates, riparian plants, and fish. The use of the census data for biological indicators is still under development.