Lake Sai is one of the Fuji Five Lakes (Fujigoko), which is the famous inhabitation of Fuji Spherical Moss. It was formed about 1200 years ago along with the eruption of Mt. Fuji. There is the Fuji Sea of Forest which is the deepest forest in Japan right next to Lake Sai.
Because the tourism is not being proceeded well, there are lots of natures are preserved. Hotels and camping lodge have many facilities for sports activities, therefore many school clubs spend summer vacation for training.