Rising flocs in the sedimentation tanks have been a problem from the very beginning at the plant in Tamara. We initially thought that the rising flocs were due to overdosing with alum, but the rising lfoc problem persisted and the very high rise rate of the flocs suggests that they are being lifted by air bubbles. The water source for Tamara is a mountain stream below a large waterfall. Thus the water at the intake is likely in equilibrium with atmospheric oxygen. The supersaturation with oxygen most likely occurs in the transmission line since some sections of the pipeline carry a mixture of air and water into regions of high pressure.