Water fronts were observed at the boundary between river and lake. These underwent considerable deformation due to the influence of the lake/land breezes. The mixing of the two water masses was promoted by the front deformation causing a water mass exchange and consequently river water was already diluted before leaving the river mouth. Whether the inflowing river overflows the lake surface or underflows along the bottom, depends on the temperature (density) difference between the water bodies under calm or weak wind conditions. In the case of an overflow the river water tended to mix with the lake water. Conversely, in the case of an underflow, particularly after heavy rain, river water tended to stay on the bottom with little vertical mixing. Water mass analysis using a temperature-conductivity diagram showed that immediately after heavy rains, river water mixed with rather shallow lake water around the river mouth and moved along the bottom with only little further mixing with the deep lake water.

Sudden rises of conductivity together with decreases in temperature were almost simultaneously recorded at some anchor stations located 1 km offshore. These changes are due to the appearance of a front advancing offshore and could be seen when drawing progressive vector diagrams. The actual distribution of conductivity was in general complicated near the river mouth; however, a simple or regular conductivity distribution could be extracted by averaging the individual values. Assuming that the actual distributions consisted of regular (steady) and irregular (fluctuating) distributions. The coefficient of longitudinal diffusion along the river was estimated 3.4 x 10⁴ cm² s^-1.