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Chichibu-Tama-Kai NP, Tokyo
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During the severe 2026 drought, the reservoir fell below 40% and revealed a dam-era quarry platform submerged since 1957. Lake Okutama can hide traces of an entire working landscape.
Local lore says an injured crane healed at Tsurunoyu, the hot spring now beneath the lake. Submerged in 1957, its source was pumped back to life in 1991; tankers deliver the water to local inns.
Residents displaced by the dam kept Ogouchi's Kashima Odori alive: 6 male dancers wear women's dress, performing 11 pieces. The tradition was inscribed with UNESCO's Furyu-odori in 2022.
Ogouchi Shrine above the lake gathers 9 shrines from settlements flooded by the reservoir. Its treasures include a Zao Gongen image bearing an ink inscription dated 1284—673 years before the dam was completed.
A dedicated railway linked Hikawa Station (now Oku-Tama) with the dam site at Mizune. From 1952 to 1958, it moved about 965,000 tonnes of cargo for the project.
Some of Ogouchi Dam's heavy equipment had already worked at Hoover Dam: Tokyo imported used crushing, concrete-mixing and 25-ton cable-crane gear, then expanded the system with Japanese machines.
The lake's everyday name was chosen publicly: in October 1957, a call for names selected “Okutama-ko” (Lake Okutama), just weeks before Ogouchi Reservoir was completed in November.
Lake water takes a detour before reaching taps: it first generates electricity at the station below the dam, then joins the Tama River. Tokyo withdraws it at intakes about 34–36 km downstream.
Building the reservoir displaced 945 households, and 87 people died in construction-related accidents. Work began in 1938, stopped during the war, and finished in November 1957 after more than 19 years.
The forests feeding Lake Okutama have been managed for Tokyo's water since 1901—56 years before the dam was completed. The water-source forest now spans 25,000 hectares across 4 municipalities.
In a 2018 net survey beside Tozura Floating Bridge, tiny sugomoroko led the catch with 123 fish—well ahead of honmoroko (39) and ugui (26). Tokyo tracks the lake's changing fish mix every 3 years.
The lake's 2 famous “drum bridges” once really floated on metal drums. Their modern floats are hollow, drum-shaped resin and metal, and the pedestrian bridges may be removed when water levels fall.
The lake had a soundtrack before it existed: “Kotei no Furusato” (“Hometown of the Lake Bottom”) was released in 1937, before filling began. A monument to the song was erected beside the reservoir in 1966.
