This paper describes the experimental investigation of pollutant dispersion by use of Osaka Bay model.
　This experiment aims to investigate the contribution of main sources of water contamination to the bay.
　Contribution ratios of these sources are known through single-point-injection tests. The north-west part of the bay is influenced by the load from the mouth of the Yodo River, and the south-east part of the bay is influenced by one from Osaka Port, in both case of present geographical condition and of future one. Contribution ratios of other release points are small and several percents at most.
　The values of the ratios are, however, increased to some degree in the future condition tests.
　Linear superposition of dye concentration distribution is confirmed to be reasonable if the experimental repeatability is attained among each runs of same conditions.