Lake Jonuma is a long, narrow lake located in the eastern part of Tatebayashi City, Gunma Prefecture. Closely connected with the area’s history, culture, and natural environment, it is one of Tatebayashi’s important scenic and tourism attractions.
In the past, the lake served as a natural defensive barrier for Tatebayashi Castle, playing an important role in the development of the castle and surrounding castle town. Today, it is a popular place to enjoy seasonal flowers, beautiful waterside scenery, and outdoor activities, providing a relaxing retreat for both local residents and visitors.
Lake Jonuma is also an important part of “SATO-NUMA,” the collective name for the lakes and wetlands scattered throughout Tatebayashi. In 2019, the SATO-NUMA landscape was recognized as a Japan Heritage site by the Agency for Cultural Affairs. The lake represents the close relationship between history, nature, and everyday life that has shaped Tatebayashi over the centuries.
Lake Jonuma stretches approximately 3.8 km from east to west while measuring only about 0.2 km from north to south. Its shoreline is approximately 8 km long, and the average depth is around 1.5 meters.
The lake is fed by the Tsuruda River, which flows through Tatebayashi from east to west. Despite being close to the city center, Lake Jonuma retains a rich waterside environment.
Walking paths and parks have been developed around the lake, making the area suitable for walking, jogging, and cycling. Boats and sightseeing vessels can often be seen on the water, while anglers gather along the shoreline, creating a peaceful lakeside atmosphere.
Approximately 550 years ago, when Tatebayashi Castle was built, Lake Jonuma was used as a natural outer moat. Its long east-west shape formed a natural defensive line around the castle and helped prevent enemy forces from approaching.
For this reason, the lake came to be known as a “defensive lake.”
During the early modern period, Tatebayashi Castle became an important strategic stronghold for the defense of Edo. Sakakibara Yasumasa, one of the Four Heavenly Kings of Tokugawa Ieyasu, became lord of the castle, and later Tokugawa Tsunayoshi, who would become the fifth shogun of the Tokugawa shogunate, also served as its lord.
The castle town subsequently developed significantly. Moats and earthen ramparts were constructed around the castle, creating a fortified urban landscape centered on Lake Jonuma.
For centuries, Lake Jonuma has been associated with a legend that a dragon god lived in the lake. The waters were regarded as mysterious and sacred, and people were traditionally warned against approaching them without good reason.
Even today, wells associated with this dragon-god legend remain in the former castle town, preserving an intriguing part of Tatebayashi’s traditional culture and folklore.
Another famous story connected with the lake is the Legend of Tsutsuji. According to the tale, around 400 years ago, a woman named Otsuji was beloved by the dragon god and ultimately threw herself into Lake Jonuma.
Moved by the tragedy, local people are said to have planted azaleas on a hill overlooking the lake. The area eventually became known as Tsutsujigasaki, or “Azalea Cape.”
Successive lords of Tatebayashi Castle continued planting azaleas, transforming the hill into a famous flower-viewing destination. It is said that the castle lords also developed the landscape into an elaborate strolling garden, treating the hill as an artificial mountain and Lake Jonuma as its pond. The garden was reportedly opened to the public during the flowering season.
Following the Meiji Restoration and Japan’s modernization, the role of Lake Jonuma gradually changed. During the Edo period, fishing was restricted and access to the lake was limited. From the Meiji period onward, however, the waters became more closely integrated into everyday community life, supporting fishing, agriculture, and ferry transportation.
Through this process, Lake Jonuma developed into what is known as a “SATO-NUMA”—a wetland or lake closely connected to the lives of local people and maintained as part of the surrounding community.
This relationship between people and water is an important part of Tatebayashi’s cultural identity and is one reason the area’s wetlands have been recognized as a Japan Heritage site.
On the southern shore of Lake Jonuma lies the famous Tsutsujigaoka Park. More than 10,000 azalea plants grow throughout the park, creating a spectacular display of color in spring.
The annual Azalea Festival, held from around April through May, attracts many visitors and has made the area one of Tatebayashi’s best-known flower-viewing destinations.
Near Lake Jonuma are the ruins of Tatebayashi Castle, where visitors can still find traces of the former castle grounds. The site has been developed as a park and is a pleasant place to explore Tatebayashi’s history on foot.
Obiki Inari Shrine, traditionally worshipped as the guardian shrine of Tatebayashi Castle, is another attraction around the lake. The shrine is associated with stories from the Sengoku period and offers visitors an opportunity to encounter the area’s history and legends.
The area around Lake Jonuma is also home to historic Buddhist temples such as Zendoji Temple and Zenchoji Temple. Their quiet grounds are well suited to leisurely walks and provide further opportunities to discover Tatebayashi’s religious and cultural heritage.
Lake Jonuma offers beautiful scenery throughout the year. Cherry blossoms and azaleas appear in spring, Japanese irises bloom in early summer, and lotus flowers cover sections of the water in summer.
The lotus flowers are generally at their best around late July, when large areas of the lake become covered with beautiful blossoms.
During the paid admission period for Tsutsujigaoka Park, ferry boats operate between the Obiki Shrine entrance and Zenchoji Temple and the park, providing a charming way to travel across the water. During the lotus season from July through August, sightseeing boats also operate, allowing visitors to enjoy the scenery from the lake itself.
Lake Jonuma is also known as a fishing destination. Fish found in the lake include carp, crucian carp, Japanese crucian carp, smelt, and dace. In the past, freshwater crabs and Kinbuna crucian carp were also commonly found, and the lake supported local fishing activities.
Changes in water quality have affected the ecosystem over time, but the lake still provides habitat for valuable aquatic plants such as water hyacinth and Kan-en-gayatsuri sedge.
In winter, swans visit Lake Jonuma to spend the season. They can generally be seen from around mid-November through early March, adding another seasonal attraction to the lakeside landscape.
Lake Jonuma once experienced serious water-quality problems, including the appearance of algal blooms and unpleasant odors during summer. Various initiatives have therefore been introduced to restore and protect the lake’s environment.
These measures include purification using plants grown on floating islands, treatment using contact materials, the use of microbubble systems, and filtration involving charcoal and microorganisms.
In 2010, a Nature Restoration Council was established for the first time in Gunma Prefecture under the Natural Restoration Promotion Act, together with the council for nearby Lake Tatara. These initiatives continue to promote the recovery and conservation of the local aquatic environment.
Lake Jonuma is relatively easy to reach. By public transportation, it is approximately a 20-minute walk from Tatebayashi Station on the Tobu Isesaki Line.
By car, the lake is approximately 10 minutes from Tatebayashi Interchange on the Tohoku Expressway, making it accessible from many parts of the Kanto region.
Lake Jonuma is one of Tatebayashi’s defining attractions, bringing together history, nature, culture, and everyday life. Its waters once helped protect Tatebayashi Castle, while later becoming an important part of the community’s livelihoods and the SATO-NUMA tradition.
Today, visitors can enjoy seasonal flowers, peaceful waterside scenery, historic sites, traditional legends, wildlife, and boat rides in a single destination.
Whether exploring the lake on foot, viewing the azaleas and lotus flowers, or discovering the historic sites around its shores, Lake Jonuma offers a relaxed way to experience the natural and cultural character of Tatebayashi.