We conducted in-situ measurement to find effects of stream discharge variation on attached algae on three types of substrates at four stations, which are located at both lower and upper reach than dams, in the upper Chikugo River, so-called the Ohyama River, in 2011. During the measurement period (May-June), a single small scale flushing occurred. Thus, we especially analyzed effects of the small flushing on amount and species of attached algae. As a result of the present research, the followings are clarified: i) Attached algae on the natural stones in the lower stream from dams grew mature and decreased much more than the upper one, ii) There is a significant difference of adhesion of attached algae between a natural stone and an artificial substrate under stable flow regime in the lower stream from dams, and iii) Small flushing of 20-30m3/s can show an effect of exfoliation of attached algae in some degree in the river.
