The first record by ultrasonic echo sounding on the distribution of the submerged standing trees on the bottom of Lake Onogawa is presented. Lake Onogawa is a dammed lake formed at the time of the eruption of the volcano Mt. Bandai in 1888. Since then the original vegetation of the dammed valley has remained submerged.
Many submerged standing trees are distributed on the bottom within about 600 m from the northeast end of the lake. The density of the trees in this area is sufficient to call thema submerged lake grove. The trees are sparsely distributed on the bottom of the central part of the lake, where residential and cultivated land of the submerged Onogawa Village had been located. There are no submerged trees on the bottom of the shallow southwest part of the lake, where the mudflows seems to have been deposited.
The vast surface of the submerged trees may serve as substrates and substrata for attached algae, bacteria, fungi and other organisms. The respiration of these attached organisms may accelerate the oxygen consumption, which in turn may accelerate many other anoxic processes such as denitrification, manganese and iron reductions.