In 1984, a major earthquake in the Kiso area created a landslide that dammed up a part of the Otakigawa River that flowed through Mt. Ontake. The valley and forest where the river flowed were fully submerged forming a lake now known as Lake Shizenko.
The trees that once stood tall and green in the forest have withered and now only skeletal trunks remain standing in the deep waters of the lake giving it an eerie effect. In summer, you can take a guided canoe or kayak tour of the lake.