In this paper, the results of the investigations of the Tachiyazawagawa are reported. The results are summarised as. follows:-
1. The water temperature of the river is lower than that of the Mogami (main stream) throughout the snow-melting season. The diffe-rence, lies 1.3 and 5.1.
2. The upper reaches of the river consist of the Nigorisawa, the Honsawa (the main stream) and the Akasawa. Among the three, the Nigorisawa is most influenced by the volcanic activity of Mt. Gassan, judging from the chemical analysis of the water taken from the stations in the drainage system.
3. The content of the dissolved oxygen in the water undergoes the diurnal change. The relation between the oxygen content and the water temperature nearly shows the negative correlation.
4. The chloride content of the river decreases regularly with the increase of the flow except during the snow-melting season.