Lake Marunuma is a beautiful lake located in Katashina Village, Tone District, Gunma Prefecture. Surrounded by magnificent mountain scenery, it is known as a scenic destination where visitors can enjoy the changing landscapes of every season.
The surrounding area is part of Nikko National Park, and its rich natural environment attracts visitors throughout the year. In 1950, Lake Marunuma was selected as the top destination in the lakes and marshes category of the New Top 100 Tourist Destinations of Japan, together with nearby Lake Sugenuma, also in Katashina Village. This recognition helped introduce the lake’s beauty to people throughout Japan.
Lake Marunuma was formed by volcanic activity around Mount Nikko-Shirane. Andesitic lava flowing from the Shirane volcano blocked a valley and obstructed the course of the Otaki River, creating the lake.
Originally, Lake Marunuma and neighboring Lake Ojiri formed a single body of water. However, changes in water levels associated with hydroelectric power generation eventually separated the two lakes.
In 1921, the Marunuma Dam was constructed for hydroelectric power generation, raising the lake’s water level and changing its shape into the elongated north-south form seen today.
Approximately 94% of the shoreline remains natural, with relatively few artificial structures. As a result, the area retains much of its pristine, natural appearance.
The lake is surrounded by rich forests containing Japanese beech, Japanese oak, Maries’ fir, and Veitch’s silver fir. In early summer, fresh green foliage is reflected on the surface of the lake, while in autumn, brilliant colors spread across the surrounding landscape and are mirrored in the water.
The peaceful beauty of the scenery attracts many visitors and has also made Lake Marunuma a popular destination for photography enthusiasts.
In winter, the lake can freeze completely and is generally covered with ice from around mid-December until early May. Snowfall can reach approximately 3 meters, creating a spectacular winter landscape during the coldest months.
However, National Route 120, also known as the Konsei Road, is closed during winter, generally from late December through late April. Visitors should check road conditions and opening information before planning a trip.
Lake Marunuma is known for fish such as rainbow trout, kokanee salmon, and smelt. It is particularly popular as a destination for lure and fly fishing.
The lake’s nutrient-rich environment supports abundant plankton, contributing to a diverse aquatic ecosystem where various fish species can reproduce naturally.
Marunuma Onsen is located near the lake, allowing visitors to enjoy a relaxing hot spring bath after fishing or hiking. This combination of outdoor activities and hot spring relaxation is one of the area’s attractions.
Lake Ojiri, located south of Lake Marunuma, is a tranquil lake also known as Hyotan-numa, or “Gourd Lake.” Like Lake Marunuma, it lies within Nikko National Park and retains a particularly natural landscape with little evidence of human development.
Lake Ojiri was formed by volcanic activity associated with the Nikko-Shirane volcanic complex. Lava filled the former course of the Otaki River, eventually creating a natural dam and forming the lake.
The entire shoreline is surrounded by natural forest, with no artificially constructed shoreline. Steep cliffs are found in many areas, helping preserve a landscape that retains a sense of its original, untouched character.
The forests around Lake Ojiri are dominated by Veitch’s silver fir, together with Erman’s birch and Japanese white birch. Large Japanese horse chestnut and Japanese wingnut trees can also be found in the area.
On rocky areas at higher elevations, Hakusan rhododendrons and Azuma rhododendrons bloom from spring into early summer, adding delicate flowers to the rugged mountain scenery.
The quiet surroundings provide an excellent setting for nature observation and forest bathing, allowing visitors to experience the peaceful atmosphere of a natural mountain forest.
From JR Numata Station or Jomokogen Station, take a Kan-Etsu Kotsu bus and get off at Kamada. Transfer to another bus and get off at Marunuma Onsen Kanko-so.
Lake Marunuma is approximately 85 minutes from the Numata Interchange of the Kan-Etsu Expressway via National Route 120, the Konsei Road.
Please note that the road is closed during the winter season, so visitors should check the latest road conditions before traveling.
Lake Marunuma and Lake Ojiri are valuable natural sites that preserve the distinctive landscapes and ecosystems created by volcanic activity in the Katashina area.
The reflections of seasonal colors on the lake, quiet primeval forests, opportunities for fishing and nature observation, and nearby hot springs offer many different ways to enjoy the area.
For visitors exploring Katashina Village, a visit to these lakes provides an opportunity to experience the peaceful beauty, geological history, and rich natural environment of Japan’s mountain landscape.