Rokaku Lake is a beautiful man-made lake created by Minouchi Dam on the Sai River in Nagano City. Surrounded by mountains and forests, the lake offers a peaceful landscape that changes dramatically with the seasons.
The name “Rokaku Lake” was given by Ikuma Arishima, the Japanese painter who had a deep affection for this region. The name evokes an image of cranes gracefully moving across the surface of the water, reflecting the serene and poetic scenery that Arishima admired.
Rokaku Lake can be enjoyed from the water as well as from the shore. Visitors can experience activities such as traditional Japanese sightseeing boats, canoeing, and stand-up paddleboarding (SUP), offering a different perspective on the surrounding landscape.
Each season gives the lake a distinctive character. Cherry blossoms add color in spring, fresh green foliage surrounds the water in summer, brilliant autumn leaves cover the mountains in fall, and snow creates a quiet winter landscape. The changing scenery makes the lake an appealing destination throughout the year.
Every year on August 15, a traditional Bon-period event takes place around the lake, featuring lantern floating and a fireworks display.
As illuminated lanterns drift across the water and fireworks light up the night sky, their reflections create a memorable and atmospheric scene. It is one of the area’s most distinctive summer traditions.
Rokaku Lake was created by Minouchi Dam, a concrete gravity dam located on the Sai River within the Shinano River system. The dam is approximately 25.3 meters high.
The facility is operated for hydroelectric power generation and supplies water to the Minouchi Power Station. Its maximum generating capacity is 31,600 kilowatts, making it an important part of the region’s hydroelectric infrastructure.
The electricity generated by the dam contributes to the energy infrastructure supporting communities and industries in Nagano Prefecture. At the same time, the dam and its reservoir have become part of the landscape of the Sai River valley.
The facility also has a history closely connected with the development of hydroelectric power in the region and the difficult circumstances surrounding its construction during the wartime period.
The history of the Minouchi Power Station dates back to 1917, when Tosin Electric became interested in using the Sai River for hydroelectric generation and applied for water rights under the name “Saigawa Hydroelectric Power.”
Other electric companies, including Nagano Electric Light, Shinano Electric, and Suwa Electric, were also competing for development rights. In 1927, permission was formally granted to Saigawa Electric.
Construction began in 1939 and faced numerous technical and environmental difficulties. Explosives were used during excavation, while innovative measures were required to deal with water leakage caused by underground cavities. In one unusual solution, sawdust was injected into the ground to help control the leakage.
The project also suffered repeated flooding. In 1941, two major floods washed away construction materials, causing further delays and difficulties.
Despite these challenges, the generators began operating in 1943, and the power station was successfully completed.
After World War II, Tokyo Electric Power took over operation of the Minouchi Power Station. Additional hydroelectric facilities were subsequently developed along the Sai River, including the Taira and Ikusaka power stations upstream and the Sasahira and Otagiri power stations downstream.
Today, the facilities are managed together from the Saigawa Integrated Control Center in Kamijo, Shinshu-Shinmachi. Equipment has also been upgraded over the years to improve reliability and address aging infrastructure, with the Minouchi Power Station now capable of producing up to 31,600 kilowatts.
Upstream from Minouchi Dam lies Kumero Gorge, a scenic area designated as a place of scenic beauty by Nagano Prefecture. The gorge is crossed by Kumero Bridge, which is also mentioned in Shinano no Kuni, the official song of Nagano Prefecture.
The gorge was once known for the powerful current of the Sai River rushing between unusual rock formations. Local legends, including a story involving a human sacrifice during the construction of the bridge, have also become part of the area’s folklore.
From central Nagano City, visitors can reach Minouchi Dam by following National Route 19 along the Sai River. Other dams, including Otagiri Dam and Sasahira Dam, are located nearby, making the area interesting for travelers who enjoy exploring Japan’s river infrastructure and dam landscapes.
The construction of the power facilities came at a heavy human cost. Thirty-six workers lost their lives during the construction process.
A memorial monument near the dam commemorates those who died. The site provides a quiet place to reflect on the people who worked on the demanding project and the history behind the infrastructure that remains in operation today.
From central Nagano City, follow National Route 19 along the Sai River toward Shinshu-Shinmachi and Minouchi Dam. The surrounding area can be combined with visits to nearby dams and scenic attractions for a leisurely drive through the Sai River valley.
From Nagano Station, buses operated by Alpico Kotsu, formerly known as Kawanakajima Bus, travel toward Shinmachi-Oharabashi. The nearest bus stop to the dam is Oizawa Iriguchi.
Rokaku Lake and Minouchi Dam offer more than a beautiful waterside landscape. The lake reflects the colors of each season, while the dam and power station tell the story of hydroelectric development along the Sai River.
A visit can combine lake activities, seasonal scenery, local history, engineering heritage, and nearby natural attractions. The connection with painter Ikuma Arishima adds an artistic dimension, while the memorial reminds visitors of the human effort and sacrifice involved in creating the infrastructure.
For travelers exploring the quieter western areas of Nagano City, Rokaku Lake provides a peaceful alternative to the city’s major tourist attractions and a chance to discover the landscape and history of the Sai River valley.