Abstract
Watarase Reservoir, located in Kanto plain in the central part of Japan, has been suffering from the problem of moldy smell in drinking water supplied from the reservoir since its commencement in 1990. The cause of the moldy smell is 2-MIB (2-methylisoborneol) produced by Phormidium sp. In order to reduce Phormidium taxa, we have conducted field experiments to test the effectiveness of water level drawdown and bed desiccation of the reservoir during early spring. The 9-years trial indicated that the reservoir bed exposure to the air and the sunlight reduced the annual maximum concentration of 2-MIB. The bottom desiccation has an effect of tormenting Phormidium taxa. While the synchronized observations of algal biomass and 2-MIB concentration suggested that the production of 2-MIB extremely decreased if the season of Phormidium growth was late such as after August. The method of water level control could make an effective measure against 2-MIB problem of drinking water caused by bluegreen algae.
