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Chichibu-Tama-Kai NP, Tokyo
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Ogouchi had its own freight railway: it linked Ome Line’s Hikawa Station with the dam site at Mizune. From 1952 until it stopped in May 1958, it hauled about 965,000 tonnes of freight.
The old Tsuru-no-yu spring was submerged when the reservoir filled, but the community revived it in 1991. Today, its water is supplied to local inns and shops.
After the reservoir covered the villages where Ogouchi’s Kashima Odori was performed, displaced residents kept it alive. The dance is now a national Important Intangible Folk Cultural Property and part of UNESCO’s 2022 Furyu-odori listing.
In October 1957, while the dam project was nearing completion, a call for reservoir names selected “Okutama-ko”—the familiar name still used for the officially named Ogouchi Reservoir.
Objects from villages later covered by the reservoir preserve a record of old Ogouchi life: 347 tools and household items were collected, including 237 connected with work and livelihoods. The collection is nationally designated.
At 149 m tall, Ogouchi was a major leap for Japanese dam-building. Engineers had little domestic experience with dams over 100 m, so they studied translated construction reports from America’s Boulder Dam.
Before the reservoir filled, 7 fish species were recorded in this stretch of river. Later surveys identified 31 species in Lake Okutama, including fish that were stocked and others that arrived unintentionally.
Water released from Ogouchi first generates electricity at a power station below the dam. It then flows about 34 km downstream to a water intake, before traveling toward Tokyo’s reservoirs and treatment plants.
Construction began in 1938, stopped in 1943 as the war intensified, and restarted in 1948. Concrete was poured day and night until 1957; the dam contains 1,675,680 m³ of it.
Rain and snow feed Ogouchi from a watershed of about 263 km²—roughly 40% of Tokyo’s 23 wards in area. About 60% of that watershed is Tokyo-managed water-source forest.
Creating the reservoir required 945 households to move, and 87 workers died during construction. Tokyo’s Water Bureau records both losses in its history of the dam.
Even Ogouchi could not prevent Tokyo’s 1964 drought crisis: the reservoir was nearly exhausted, and water restrictions reached 50% as the city prepared for the Olympic Games.
Ogouchi’s Kashima Odori features 6 men dancing in women’s kimono and preserves 11 traditional pieces. The Agency for Cultural Affairs notes that its movements carry traces of early kabuki dance.
