Abstract
The organic pollution of Arakawa River in Kofu city was assessed using the diatom assemblage index to organic pollution (DAIpo). The DAIpo values were 98, 45 and 45 at the up-, mid- and downstreams, respectively. BOD at the mid- and downstreams were threefold higher than at the upstream. Among the dominant diatoms at the upstream, Encyonema silesiacum and Hannaea arcus var. hattoriana, were also abundant in 1977, suggesting little change of the diatom species composition during 30 years despite the dam construction.
