Lake Nakaumi is one of the largest and most distinctive lakes in the San’in region of western Japan. Stretching across Matsue and Yasugi in Shimane Prefecture and Yonago and Sakaiminato in Tottori Prefecture, it forms a vast water landscape closely connected with the lives, industries, and natural environment of the surrounding communities.
With a surface area of approximately 86 to 92 square kilometers and a shoreline of about 83 kilometers, Lake Nakaumi is generally regarded as Japan’s fifth-largest lake by area. Its broad waters are surrounded by the Shimane Peninsula, the Yumigahama Peninsula, and several distinctive islands, creating a landscape that changes beautifully with the seasons.
Lake Nakaumi is a lagoon formed when a bay that once opened directly to the Sea of Japan became partially enclosed by the development of sandbars. Today, the lake remains connected to the sea through the Sakai Channel on its eastern side, while its western side connects to Lake Shinji through the Ohashi River.
This unusual water system makes Lake Nakaumi and Lake Shinji one of Japan’s relatively rare examples of interconnected brackish lakes. Water moves between the two lakes and the Sea of Japan, allowing freshwater and seawater to influence each other and creating a distinctive environment for aquatic life.
Lake Nakaumi lies between the long, narrow Yumigahama Peninsula and the Shimane Peninsula. Yasugi and Yonago lie to the southeast, Sakaiminato and the Mihonoseki area to the northeast, and Matsue to the west. The lake therefore forms an important geographical link between the two prefectures.
Several islands are scattered across the lake, including Daikonshima and Eshima in Matsue’s Yatsuka area and Kamejima in Yasugi. Each contributes to the distinctive scenery of Lake Nakaumi.
Daikonshima Island was formed through volcanic activity and is particularly famous for its cultivation of peonies and medicinal ginseng. The island’s fertile volcanic soil and mild climate have supported agriculture that has become an important part of its identity.
Eshima Island is connected with Sakaiminato by the Eshima Bridge. The bridge rises dramatically above the surrounding landscape and has become a recognizable feature of the area.
Lake Nakaumi has a maximum recorded depth of approximately 18.4 meters. Earlier measurements placed the deepest point at 17.1 meters, but subsequent surveys revised the figure. The deepest area is thought to be associated with a section that was widened during construction work connected with past land-reclamation projects.
The lake’s average salinity is approximately half that of seawater, making it considerably saltier than neighboring Lake Shinji. This difference in salinity contributes to differences in the species of fish and other aquatic organisms found in the two connected lakes.
At the same time, Lake Nakaumi supports both marine and freshwater organisms, including Japanese freshwater clams. This mixture of species is one of the defining characteristics of a brackish-water ecosystem.
One of Lake Nakaumi’s greatest natural attractions is its importance as a habitat for migratory birds. Each year, more than 75,000 geese and ducks are estimated to visit the area, making it one of the largest wintering grounds for waterbirds in Japan.
More than 1,000 whooper swans may gather around Lake Nakaumi during the winter season. The lake is regarded as the southern limit of the major wintering grounds for this species in Japan.
Other birds include common pochards, tufted ducks, and scaups. The lake’s importance extends beyond Japan, as its wetlands support a significant proportion of the global populations of some waterbird species.
For birdwatchers and nature photographers, winter is an especially rewarding time to visit. The sight of white swans and large flocks of ducks resting on the calm water creates a peaceful scene characteristic of the San’in winter landscape.
Lake Nakaumi was designated as a national wildlife protection area in 1974. In 2005, it was registered as a Ramsar Convention wetland together with Lake Shinji, recognizing the international importance of these wetlands for biodiversity and migratory birds.
More than 260 species of birds have been recorded in the Lake Nakaumi area, including species listed in Japan’s environmental red data resources. The lake is also home to an exceptionally diverse range of aquatic organisms, with more than 160 species of crustaceans recorded.
These figures illustrate why Lake Nakaumi is valued not simply as a scenic lake but as an important natural environment supporting a wide variety of species.
The area around Lake Nakaumi offers several opportunities to experience its wildlife. Yonago Waterbird Sanctuary and Hakuto Coast are particularly well known as places for birdwatching.
During winter, visitors may be able to observe whooper swans and other migratory birds resting and feeding around the wetlands. Binoculars and a telephoto camera can make it easier to appreciate the birds while keeping a respectful distance from their habitat.
The changing light over the lake also creates attractive conditions for photography. Early morning and evening can be especially atmospheric, when the calm surface of the water reflects the surrounding landscape.
Lake Nakaumi is not only a destination for wildlife observation. From summer into autumn, the lake can also be enjoyed through recreational activities such as windsurfing, water skiing, and fishing.
Cruises on Lake Nakaumi and neighboring Lake Shinji provide another way to appreciate the region. From the water, visitors can enjoy wide views of the San’in landscape while experiencing the interconnected nature of these two brackish lakes.
For an even more unusual perspective, sightseeing flights using amphibious aircraft offer views from above, allowing visitors to see Lake Nakaumi, the Sea of Japan coast, and the surrounding peninsulas and islands as a single landscape.
Fishing has long been an important part of life around Lake Nakaumi. In the 1950s, catches of ark shells, known locally as akagai or sarubō, were particularly abundant. However, catches gradually declined due in part to environmental changes such as the occurrence of red tides.
Today, fishing continues, with species such as Japanese sea bass among the important catches. Annual landings are generally around 300 to 400 tons.
The lake has also supported transportation and regional commerce. Inland ports such as Yasugi Port and Yonago Port remain connected with the economic life of the surrounding communities.
The origins of Lake Nakaumi can be traced back approximately 7,000 years to the period of the Jōmon marine transgression. At that time, rising sea levels created an extensive bay known as the ancient Nakaumi Bay.
As the Yumigahama sandbar developed and sea levels changed, the bay gradually became separated from the open sea. The modern lake was formed through this long process of geological and environmental change.
The importance of this waterway has continued throughout Japanese history. In the Izumo no Kuni Fudoki, a geographical record compiled in the Nara period, the area was described as “O no Irie”, or the inlet of O. This historical reference demonstrates that the waters of the region were already recognized as an important part of the landscape more than 1,000 years ago.
After World War II, large-scale plans were developed to reclaim parts of Lake Nakaumi and convert its water into freshwater for agricultural and other uses. These projects became the subject of extensive discussion as understanding of the lake’s environmental importance developed.
The land-reclamation project was ultimately cancelled in 2000, followed by the cancellation of the freshwater conversion plan in 2002. Facilities associated with the projects were subsequently removed, and attention shifted toward environmental restoration and sustainable regional development.
The history of these projects is an important part of understanding modern Lake Nakaumi. It illustrates the complex relationship between the needs of local communities, economic development, water management, and the conservation of natural ecosystems.
Because Lake Nakaumi is connected to the Sea of Japan and lies in a low-lying coastal region, managing water levels is an important issue. A major storm surge in 2003 produced the highest recorded water level at that time and caused flooding in parts of Yonago and Matsue.
In response, comprehensive flood-control measures have been developed, including improvements to waterways, drainage systems, and the Ohashi River, as well as other water-management projects throughout the Hii River system.
Lake Nakaumi and Lake Shinji are closely linked, yet their different salinity levels and physical characteristics create distinct environments. Lake Shinji is generally less saline, while Lake Nakaumi receives a stronger influence from seawater entering through the Sakai Channel.
Travelers who visit both lakes can therefore experience two related but different water landscapes within the same region. Together, they form an important ecological network connecting inland waterways with the Sea of Japan.
The islands and peninsulas around Lake Nakaumi provide many opportunities to experience the scenery of the San’in region. Daikonshima offers a glimpse into the area’s volcanic origins and agricultural traditions, while Eshima and the surrounding waterways reveal the close relationship between transportation, local communities, and the lake.
The broad surface of the lake also creates expansive views that change with the weather. Clear summer days bring bright blue water and open skies, while winter often brings mist, subdued light, and flocks of migratory birds.
Lake Nakaumi is a remarkable place where nature, history, transportation, fishing, agriculture, and local communities have developed together over thousands of years.
Its brackish waters support an unusual mixture of marine and freshwater life, while its wetlands provide an essential habitat for tens of thousands of migratory birds. At the same time, the lake continues to support fishing, transportation, recreation, and tourism.
For travelers, Lake Nakaumi offers a different side of the San’in region from the historic streets of Matsue or the famous sunset of Lake Shinji. Birdwatching, cruises, water sports, island sightseeing, and quiet lakeside walks each reveal a different aspect of this vast water landscape.
Each season brings a different character to Lake Nakaumi. Summer and autumn are well suited to enjoying the lake breeze and outdoor activities, while winter offers exceptional opportunities to observe migratory waterbirds.
The surrounding islands, mountains, waterways, and distant Sea of Japan create constantly changing scenery throughout the year. A visit to Lake Nakaumi can therefore be combined with sightseeing in Matsue, Yasugi, Yonago, Sakaiminato, and the wider Shimane and Tottori regions.
Lake Nakaumi is more than one of Japan’s largest lakes. It is a living landscape where freshwater and seawater meet, supporting diverse wildlife while remaining deeply connected with the lives of the people who live around it.
Together with Lake Shinji, it represents one of the defining natural environments of the San’in region. From thousands of years of geological change and centuries of human use to today’s conservation efforts, Lake Nakaumi continues to evolve as a place where people and nature coexist.