Spectacular Inspection Discharges
One of the most impressive sights at Yagisawa Dam is the inspection discharge, generally carried out between May and July each year. During this operation, water is released from the ski-jump-style spillway to test the emergency flood-discharge gates. Huge volumes of water rush down the spillway, creating powerful sprays and an unforgettable spectacle.
Many visitors come specifically to see this impressive display. The exact schedule varies from year to year, so visitors should check the latest information provided by the Japan Water Agency before planning their visit.
Nature View Yagisawa: A Disaster Prevention Museum
Next to the dam management office is Nature View Yagisawa, a disaster-prevention information center where visitors can learn about the structure and functions of the dam as well as the natural environment of the upper Tone River region.
The facility features video materials and informative exhibition panels introducing the dam and the surrounding environment. Visitors can also learn about the plants and animals found in the Okutone area. Admission is available for self-guided visits, making the facility suitable for families and educational trips.
The Four Seasons and Nature of Lake Okutone
Spring: Fresh Greenery and Snow-Capped Mountains
In spring, the mountains of the Mikuni Range still retain patches of snow while fresh green leaves begin to surround the lake. The combination of snow-covered peaks, new greenery, and the clear mountain air creates a refreshing landscape.
Summer: A Cool Mountain Lake
Because of its high elevation, the area remains relatively cool even during the height of summer. Lake Okutone is therefore popular as a summer retreat, where visitors can enjoy outdoor activities such as canoeing, boating, and fishing.
Autumn: Spectacular Fall Colors
In autumn, the forests around the lake turn vivid shades of red and yellow. The colorful foliage reflected on the calm surface of the lake creates an almost dreamlike landscape, making this a particularly popular season for photographers.
Winter: Deep Snow and Profound Silence
The Okutone area is one of Japan’s regions known for heavy snowfall. During winter, the access road to the dam is closed. The landscape becomes covered in deep snow, revealing a stark yet mysterious side of the natural environment.
Yagisawa Power Station and Energy Supply
Yagisawa Power Station uses Lake Okutone as its upper reservoir and is a pumped-storage hydroelectric power station operated by TEPCO Renewable Power. The lower reservoir is the reservoir of Sudagai Dam, and the station has a maximum authorized output of 240,000 kW.
The power station was also notable for its pioneering introduction of variable-speed pumped-storage generation technology, contributing to the development of Japan’s power-generation technology.
History and Construction of Yagisawa Dam
The idea of constructing a dam in the Yagisawa area dates back to before World War II. Several development plans were considered, including a Tokyo municipal water-supply project, Gunma Prefecture’s plans for regulating the Tone River, and Tokyo Electric Light Company’s plans for developing hydroelectric resources in Okutone.
Among these proposals, the Oze Water Diversion Plan attracted particular attention as a large-scale pumped-storage hydroelectric project. However, the plan was never realized because of issues including water-rights arrangements.
After the devastating flooding caused by Typhoon Kathleen in 1947, together with rapidly increasing water demand following the war, comprehensive flood-control and water-resource measures for the Tone River system became an urgent priority.
Full-scale construction of Yagisawa Dam began in 1959, and the dam was completed in 1967. Since then, it has played an important role as one of the major water reservoirs supporting the Greater Tokyo Area.
The Multiple Roles of Yagisawa Dam
Yagisawa Dam serves many purposes. Its flood-control function helps reduce peak flood discharge at the Yawatashima area of Isesaki City. The dam also supplies water for existing farmland, provides water for newly developed agricultural areas, and supplies approximately 340,000 tons of tap water per day to Tokyo.
In addition, the dam contributes to hydroelectric power generation. Its total storage capacity is approximately 240 million cubic meters, making it one of the largest reservoirs in the Kanto region.
A Scenic Destination as Well as an Important Infrastructure Facility
The area around Yagisawa Dam is surrounded by famous hot spring destinations, including Yunokoya Onsen, Takaragawa Onsen, and Minakami Onsen. Visitors can therefore combine a visit to the dam with a relaxing hot spring trip.
Yagisawa Dam, together with Naramata Dam, has also been selected as one of the 100 Dam Lakes of Japan. The area offers a fascinating opportunity to experience the harmony between advanced civil engineering and the natural beauty of the mountains.
The distinctive curved form of the arch dam is particularly impressive when viewed from directly below the dam body. The graceful structure appeals to visitors interested in architecture and civil engineering, while the surrounding natural forest gives Lake Okutone a peaceful and mysterious atmosphere.
With its tranquil water surface and magnificent mountain scenery, Lake Okutone provides a relaxing setting where visitors can appreciate the beauty of nature throughout the year.
Access and Important Information
Yagisawa Dam can be reached from the Minakami Interchange on the Kan-Etsu Expressway via National Route 291 and Gunma Prefectural Route 63.
However, the road is generally closed from late November until late April because of heavy snowfall. Visitors are strongly advised to check the latest road and weather conditions before setting out.
A Symbol of Nature and Advanced Engineering
Yagisawa Dam and Lake Okutone represent a remarkable combination of abundant natural beauty and advanced civil engineering. The dam is an essential facility supporting the daily lives of people in the Greater Tokyo Area, while the surrounding lake and mountains offer spectacular scenery in every season.
From the dramatic inspection discharges to the colorful autumn forests and quiet winter landscape, Yagisawa Dam offers visitors a chance to experience both the impressive scale of modern infrastructure and the pristine natural environment of Okutone.