Abstract
The assemblage in which the most abundant taxon belongs to Navicula appeared in 281 sites among 1287 sampling sites in flowing and standing waters. The number of the most abundant taxon belongs to Navicula and that of sites in where such the diatom assemblage occurred in each saprobic level are the following. From these facts, it can be seen that the taxa which belong to Navicula occur so frequently as the dominating taxon in attached diatom assemblage, and in the polluted waters than the clean waters. The dominating taxa with much frequency of occurrence are the following ten taxa; Navicula atomus var. atomus, N. gregaria, N. minima var. minima, N. mutica var. mutica, N. mutica var. goeppertiana, N. mutica var. stigma, N. mutica var. ventricosa, N. pelliculosa, N. seminulum var. seminulum, N. subminuscula.
