Shimagawa Dam: A Blue Jewel in Gunma's Mountains

Shimagawa Dam, completed in 1999, stands as a testament to engineering and natural beauty in Nakanojo, Gunma Prefecture. This concrete gravity dam was built on the Shimagawa River to control floods, generate power, and provide a stable water supply. However, it is the dam's creation of Lake Okushima that truly captivates visitors. Lake Okushima is famous for its unique 'Shima Blue' color, a mesmerizing turquoise hue caused by the diffused reflection of light and the hot spring minerals flowing into the lake. The color changes with the seasons, sunlight, and time of day, offering a different spectacle with each visit. The lake's circumference is approximately 4km, inviting visitors to stroll along its banks, rent a bicycle, or drive around (though driving is not possible in winter). Around Lake Okushima, you'll find several parks and observation decks offering panoramic views of the dam, lake, and surrounding mountains. Inatsutsumi Seseragi Park features a boardwalk that leads down to the water's edge, while Hinamimi Park offers an overwhelming perspective of the dam's enormity. For those seeking more active pursuits, Green Discovery offers canoeing and SUP (Stand Up Paddleboarding) experiences on the lake. The Shimagawa Dam itself is an impressive structure, standing 89.5 meters high and 330 meters long. While internal tours of the dam are available, they require advance booking (at least two weeks prior) and are conducted in Japanese only, with a minimum group size of six. However, visitors can obtain a free dam card at the Shimagawa Dam Office (weekdays only) as a souvenir. Located at the innermost part of Shima Onsen, the dam and lake are easily accessible by car. From Nakanojo Station, it's about a 45-minute bus ride to Shima Onsen, followed by a 15-minute drive to the dam. The area offers ample parking, making it convenient for those arriving by car.