Lake Ashinoko is a caldera lake located in Hakone, Ashigarashimo District, Kanagawa Prefecture. Surrounded by the natural scenery of the Hakone mountains, it is one of the area’s best-known sightseeing destinations and attracts visitors throughout the year. The lake was formed through volcanic activity and lies at an elevation of approximately 720 meters above sea level. Its surface area is about 7.0 square kilometers. Although its overall shape is roughly circular, the shoreline is irregular, with several bays and inlets extending into the surrounding landscape. The mountains around the lake are reflected on its surface, creating beautiful views. On clear days, visitors may also enjoy views of Mount Fuji, making Lake Ashinoko one of the most celebrated scenic spots in Hakone.
Located in southwestern Kanagawa Prefecture, Lake Ashinoko is the largest lake in the prefecture. It belongs to the Hayakawa river system, which is classified as a second-class river system in Japan. Most of the lake’s water comes from springs on the lakebed. The lake is also the natural source of the Hayakawa River, which flows northward from the area of Sengokuhara in Hakone. However, water rights for the lake belong to parties on the Shizuoka Prefecture side. As a result, water is generally not released from Lake Ashinoko into the Hayakawa River, except in emergencies such as periods of excessive water levels. The lake is surrounded by sightseeing destinations and resort facilities, and its combination of mountain scenery and views of Mount Fuji makes it especially popular with travelers. Lake Ashinoko is also famous as the location of the outward-leg finish and return-leg starting point of the annual Hakone Ekiden, a major university relay marathon held around the New Year.
One of the most enjoyable ways to experience Lake Ashinoko is from the water. Two sightseeing boat services operate on the lake: the Hakone Pirate Ship, operated by the Odakyu Hakone group, and the Lake Ashinoko Sightseeing Boat, operated by Hakone Yusen, which belongs to the Fujikyu group. These boats allow visitors to enjoy the lake’s scenery from the water and take in the surrounding mountains from a different perspective. On clear days, Mount Fuji may be visible across the lake. The boats depart from different piers, and the discount tickets and free passes accepted by each service may also differ. Travelers planning a cruise should therefore check the departure locations and ticket conditions in advance. The lake is also well known as a fishing destination. Rainbow trout and black bass are among the fish stocked in its waters. In particular, Lake Ashinoko is famous in the history of Japanese bass fishing: black bass were first introduced to Japan here in 1925 by Tetsuma Akaboshi.
Lake Ashinoko supports a variety of fish and aquatic animals. Species found in the lake include rainbow trout, brown trout, kokanee salmon, largemouth bass, carp, crucian carp, Japanese dace, pale chub, Japanese smelt, yamame trout, char, and other freshwater fish. The lake and its surrounding waters are also home to small aquatic creatures such as freshwater crabs and freshwater snails. These species are important not only to the lake’s natural environment but also to its fishing culture and local food traditions.
Fish from Lake Ashinoko are also enjoyed as regional specialties. Tempura made with Japanese smelt and rainbow trout is particularly well known around the lake and is popular with visitors. Another distinctive dish served in the area is a tempura rice bowl made with largemouth bass, commonly called black bass. It offers travelers an opportunity to try a fish closely associated with the lake’s fishing history.
Lake Ashinoko is surrounded by sightseeing destinations and opportunities for outdoor recreation.
Located on the eastern shore of the lake, Hakone Shrine is a historic shrine famous for its torii gate standing in the water. The shrine grounds also offer beautiful views of the lake and the surrounding mountains. It is one of the most recognizable sights in the Hakone area.
Cruise boats operate on Lake Ashinoko, allowing visitors to appreciate the natural scenery from the water. On sunny days, the view may extend to Mount Fuji, creating a particularly memorable experience.
Several hiking routes can be found around the lake. Visitors can walk along the lakeshore and explore the natural environment of Hakone. Routes that follow the lakeside are especially popular with people who want to enjoy the scenery at a relaxed pace.
Hakone is one of Japan’s best-known hot spring destinations, and many hot spring inns and accommodation facilities are located near Lake Ashinoko. Some offer baths with views of the lake, allowing guests to relax while enjoying the surrounding landscape.
The water rights for Lake Ashinoko belong to the Shizuoka Prefecture Ashiko Water Rights Association, which consists of Susono City, Nagaizumi Town, Shimizu Town, and Gotemba City in Shizuoka Prefecture. The Kanagawa Prefecture side does not have the right to use the lake water. Emergency releases may nevertheless be carried out when necessary. Wastewater management is another important aspect of protecting the lake and its surroundings. Wastewater from the lakeside communities of Hakone, Motohakone, Kojiri, and Sengokuhara is treated at the Sengokuhara Water Purification Center before being discharged into the Hayakawa River. Kanagawa Prefecture is also responsible for measures to prevent water pollution, helping to protect the lake’s environment.
Lake Ashinoko lies within the caldera of the Hakone volcano. Approximately 3,000 years ago, Mount Kamiyama, one of the central volcanic cones within the caldera, experienced a steam explosion and pyroclastic flow. The resulting collapse of the mountain blocked the Hayakawa River within the caldera, creating the lake. The lake is also associated with a famous religious legend. In 757, during the Tenpyō-hōji era, a Buddhist monk named Mangan established Hakone Shrine. According to tradition, he later subdued a nine-headed dragon that had been tormenting the people around the lake. He then built a shrine at the site of what is now the main sanctuary of Kuzuryu Shrine and enshrined the dragon as a guardian deity. This legend remains an important part of the religious and cultural heritage of the Hakone area.
During the Edo period, an important irrigation project was undertaken to bring water from Lake Ashinoko to Fukara Village in Sunto District, Suruga Province, in what is now Susono City, Shizuoka Prefecture. The village headman, Gennojo Oba, led the project to construct a tunnel through the outer rim of the Hakone mountains. The Fukara Irrigation Channel was completed in 1670, the tenth year of the Kanbun era. Today, this waterway forms the Fukara River, a tributary of the Kise River in the Kano River system. It has been selected by Japan’s Ministry of Agriculture, Forestry and Fisheries as one of the country’s 100 notable irrigation waterways, in recognition of its importance as an outstanding example of traditional water engineering. During the Edo period, both Hakone and Fukara belonged to the Odawara domain, so there was no dispute over water rights between the two areas. After the abolition of the feudal domains and the establishment of the prefectural system, however, the area was divided between Kanagawa and Shizuoka prefectures, leading to disputes over ownership and use of the lake water. The issue was eventually settled through a court ruling in the Taisho period, which recognized Shizuoka Prefecture’s water rights.
Sightseeing boat services helped establish Lake Ashinoko as a major tourist destination. In 1911, a sightseeing boat service began operating on the lake. The business later became associated with the Seibu Group. In 1925, black bass were introduced to the lake for the first time in Japan, contributing to its reputation as a fishing destination. In 1950, Hakone Sightseeing Boat, the predecessor of today’s Hakone Pirate Ship service, began operating. These developments further increased the lake’s appeal as a place for sightseeing and recreation. In October 2019, however, Lake Ashinoko overflowed during Typhoon Hagibis, also known as Reiwa 1 East Japan Typhoon or Typhoon No. 19. The flooding caused damage to ports and tourist facilities around the lake.
Travelers commonly reach Lake Ashinoko by using the Hakone Tozan Railway and connecting bus services. From Hakone-Yumoto Station, the lake area can generally be reached by bus in approximately 30 minutes. There are also numerous sightseeing facilities and restaurants around the lake, making it convenient to spend time exploring the surrounding area. Visitors arriving by car should be aware that parking areas can become crowded, particularly during busy sightseeing periods, and that parking fees may apply.
Lake Ashinoko is a volcanic lake where beautiful mountain scenery, views of Mount Fuji, and the cultural heritage of Hakone come together. Visitors can enjoy the landscape from the lakeshore or aboard a sightseeing boat, explore nearby shrines and hiking routes, try local fish dishes, and relax at hot spring inns. The scenery changes with the seasons, offering different experiences throughout the year. Whether visiting for a cruise, fishing, hiking, or simply taking in the view, Lake Ashinoko is an excellent place to discover the natural and cultural attractions of Hakone.