The microbial and chemical analysis of water samples collected at several staitions in the rivers and estuaries in Osaka City was made from April 1974 through March 1977 at monthly intervals over a 3-yr period.
Fluctuation in the numbers of heterotrophic bacteria by the standard plate count at 37°C and coliform bacteria depended on the concentration of organic substances as pollutant at each station and on water temperature. Both bacterial numbers reached the maximum at the most polluted station. During the dilution process of the river water at the estuaries the decrease in the numbers of coliform bacteria was silightly larger than that of heterotrophic bacteria. As to the seasonal distribution of bacteria, the maximum number of heterotrophic bacteria had been observed during the summer.