Western Lake, sometimes Saiko, is the one of the Fuji Five Lakes and located in the town of Fujikawaguchiko in southern Yamanashi Prefecture near Mount Fuji, Japan.

It is the fourth of the Fuji Five Lakes in terms of surface area, and second deepest, with a maximum water depth of 71.1 metres (233 ft). Its surface elevation of 900 metres (3,000 ft) is the same as for Lake Motosu and Lake Shōji, confirming that these three lakes were originally a single lake, which was divided by an enormous lava flow from Mount Fuji during an eruption from 864 to 868 AD. The remnants of the lava flow are now under the Aokigahara Jukai Forest, and there is evidence to indicate that these three lakes remain connected by underground waterways.

The lake is located within the borders of the Fuji-Hakone-Izu National Park.

Japan is divided into 47 prefectures, which form the first level of jurisdiction and administrative division in their governmental structure. They consist of 43 prefectures proper, two urban prefectures (Osaka and Kyoto), one "circuit" or "territory", Hokkaido) and one "metropolis", (Tokyo).

While Japan is a unitary state, the central government delegates many functions (such as education and the police force) to the prefectures and municipalities, but retains the overall right to control them. Although local government expenditure accounts for 70 percent of overall government expenditure, the central government controls local budgets, tax rates, and borrowing.

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