Lake Mashu, Hokkaido, Japan

Lake Locations:

Japan - Hokkaido -

Also known as:  Lake Masyu, Mashu-See, Mashu-ko

Akan National Park, established in 1934 on the island of Hokkaido, Japan, is a pristine and wild landscape. The park is known for its vibrant blue, clear caldera lakes and natural hot springs, and is divided into two sections; Lake Mashu, one of the clearest lakes in the world, is found in the Kawayu area. Total park area is 349 square miles (905 square kilometers), making up a large portion of northeastern Hokkaido, much of which is a former and still potentially active volcano. Although the last eruption of the volcano below Lake Mashu occurred about 1,100 years ago, the lake was formed around 30,000 years ago during the Holocene era, according to geologic estimates.

Lake Mashu, a natural lake that is 3.7 miles (6.0 kilometers) wide at its maximum, was formed in a caldera, which is a depression that may result from a volcanic eruption. When the magma evacuates from beneath the top of the volcano, often the weight of the volcano’s peak is too much for the now-empty magma chamber to bear. The dome then collapses into a deep concave shape, or a caldera. The lone island in Lake Mashu, called Kamiushu, is actually a lava dome that is mostly underwater. The oval-shaped island rises about 82 feet (25 meters) above the lake’s surface at its highest point.

Lake Mashu is a kidney-bean-shaped crater lake with a closed drainage basin–called an endoheic basin–which means that no rivers or streams appear to take water away from it, and no direct outlet is known. This is a curious phenomenon because two small streams feed the lake, but the water level is quite stable for most months of the year. Research has suggested that water likely seeps out through the underground volcanic vents or porous lake bed sediments to maintain the static water level. The lake’s bottom, which is peppered with pumice deposits, has been found to be very level, which is fairly common among caldera lakes.

At an average depth of 451 feet (137 meters) and a maximum depth of 694 feet (211.5 meters), Lake Mashu is one of Japan’s deepest and clearest lakes. In 1931, a measurement of the clarity of this lake’s water was recorded at 136 feet (41.6 meters) depth for maximum transparency. In the decades since, the water has remained quite clear and remarkably deep blue, but has also become home to rainbow trout and sockeye salmon, which has decreased its clarity to some degree.

National parks in Japan are governed by the Ministry of the Environment, whose purpose is to protect the unique natural resources available in this island nation, while allowing the public and visitors safe and enjoyable but limited access. For Lake Mashu, this means visitors are prohibited from approaching the lake’s shoreline, and no homes or camps are allowed along the lake; however, this rule is not difficult to enforce because 660-foot (200-meter)-high crater walls fully encircle the lake. On the western edge of the lake, an overhanging cliff dominates the crater wall. Full and lush evergreen and birch forests line the crater walls around the lake, and visitors are encouraged to use the two established viewing areas to enjoy the best views of the lake.

With its protected status and unspoiled environment, it’s no surprise that Akan National Park is home to many endangered and protected species. Visitors are likely to encounter the northern red fox, red-crowned crane, ezo deer, brown bear, black woodpecker, white-tailed eagle, Blakiston’s fish owl, and Steller’s sea eagle. The sound of cicadas and crickets is a constant music in these areas in the warmer months.

Lake Akan holds the greatest acclaim of the three caldera lakes in this national park, which is due to its unique environment that allows the endangered and protected species of green algae called marimo to grow to unusually large sizes. These globes can reach up to 12 inches (0.3 meters) in diameter, are velvety in texture, and are brilliant green in hue. A festival is held each fall in their honor–a reminder that their protection is important to the lake’s ecosystem. Although Lake Mashu, also known as Lake Masyu or Mashu-ko, is frozen over from December to April in most years, no winter sports are allowed in its vicinity. Instead, Lake Akan provides an arena for skating, ice fishing, and snowmobiling.

A local hiking trail along the crater’s rim, known as the Mashu-dake Hiking Course, is an enjoyable trek and provides stunning views of the landscape and the valley of the lake. As might be expected, cycling near the lake is also popular, as is camping in the area beyond the prohibited zone. The Mashuko Youth Hostel, situated between the lake and the town of Mashuko, is well known for its good location. Teshikago, found to the south of Lake Mashu, is the closest small city, with a population of about 8,700. The Wakoto Peninsula Campground is located on the shore of nearby Lake Kussharo, which is a caldera lake to the west of Lake Mashu worthy of a visit. With Lake Akan to the southwest, these three caldera lakes draw many visitors to Akan National Park every year. Lodging and other visitor amenities are available in nearby areas.

For visitors interested in local culture, the nearby picturesque village of Ainu Kotan is a popular destination. Cozy streets allow travelers to roam from shop to shop, browsing handmade crafts and artisan jewelry, traditional folk art, souvenirs, woodcarvings, sculptures, and fabric crafts. Cafes and restaurants feature light snacks and full meals, some of the most popular showcasing local Hokkaido culinary specialties. The local Yukar Theater presents ancient dances of the Ainu people as well as other cultural demonstrations and entertainment. The highlight of Ainu Kotan, according to many visitors, is the traditional Ainu house that has been re-created to give a glimpse into the area’s history. Included in this reproduction setting is a diverse collection of demonstrations and workshops that travelers can try or simply observe. From demonstrations on the manufacture of tools and clothing to woodcarving, cultural activities abound here and are sure to delight everyone interested in local traditions.

One of the most interesting aspects of Lake Mashu’s history is its legendary status as a cursed lake. Known by the Ainu people as the “Lake of the Devil,” Lake Mashu is said to bring bad luck to those who glimpse its serene and mirror-like surface. During the warmer months, a thick fog usually obscures the lake’s surface. It’s a truly ironic twist that most visitors never get to see this startlingly clear and brilliantly blue lake because it is so often shrouded in mist.

Things to do at Lake Mashu

  • Vacation Rentals
  • Ice Fishing
  • Campground
  • Hiking
  • Biking
  • Snowmobiling
  • Wildlife Viewing
  • Birding
  • National Park

Fish species found at Lake Mashu

  • Rainbow Trout
  • Salmon
  • Sockeye Salmon
  • Trout

Lake Mashu Photo Gallery

Lake Mashu Statistics & Helpful Links

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Lake Type: Natural Freshwater Lake, Not Dammed

Surface Area: 4,695 acres

Shoreline Length: 12 miles

Normal Elevation (Full Pond): 1,152 feet

Average Depth: 451 feet

Maximum Depth: 694 feet

Water Volume: 2,318,640 acre-feet

Lake Area-Population: 8,800

Drainage Area: 13 sq. miles

Trophic State: Oligotrophic

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Trophic State | LakeLubbers

Trophic State measures the level of algae and nutrients in a lake.

An oligotrophic lake is very clear (blue in color) and does not support much plant or fish life. A hyper-oligotrophic lake is the clearest of all lakes, and is nearly devoid of plants and fish.

A mesotrophic lake is slightly green and supports a moderate degree of plant and fish life. A lake's most desired trophic state is generally this mid-point - the mesotrophic state.

A eutrophic lake is somewhat murky and supports a large amount of plant and fish life. A hypereutrophic lake is clouded with algae, plant life, and fish life. A eutrophic or hyper-eutrophic lake can be difficult to navigate by boat - and is often an unpleasant place to swim.

The use of phosphorus-rich and nitrogen-rich fertilizer on lawns and golf courses surrounding a lake can cause it to become eutrophic or hypereutrophic.


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Catchment or Drainage Area | LakeLubbers

This is the surrounding area that drains into a lake, including land, rivers and their tributaries. This is also known as the lake's "catchment basin".

Small lakes at the highest peaks of mountains have small drainage areas. The world's oceans have the largest drainage areas.


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Lake-Area Population | LakeLubbers

This is the estimated number of people who live in a house with a view of a lake, plus those who self-describe the lake as their home, for example: "I live at Smith Mountain Lake."


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Water Residence Time | LakeLubbers

This is the estimated time that it takes for an amount of water equal to the entire volume of a lake to flow out of - or evaporate from - the lake.

Residence Time can be as short as a few days for fast-flowing small lakes, and can exceed 100 years for slow-flowing large lakes.


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Completion Year | LakeLubbers

This is the year that a reservoir was first filled to the reservoir's normal elevation - or the year that a natural lake was first dammed. A large reservoir can take more than a year to fill after its dam is first closed.

The Grand Anicut in southern India is generally considered the world's oldest dam that still operates. Grand Anicut was constructed in the second century BC. It now impounds an irrigation network that includes roughly one million acres.

You can find many of the the world's newest reservoirs on LakeLubbers. Many of the world's oldest reservoirs appear on the last page of that list.


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Water Volume | LakeLubbers

This is the estimated volume of water that a lake contains -- measured at the lake's normal elevation. By this measure, the world's largest freshwater lake is Siberia's Lake Baikal.

You can find many of the the world's largest lakes (by water volume) on LakeLubbers.

Water Volume can be measured in acre-feet, in cubic miles, or in cubic kilometers. One acre-foot is the amount of water needed to cover one acre (43,560 square feet) to a depth of one foot. One cubic mile equals 3,379,200 acre-feet. One cubic kilometer equals 810,713 acre-feet.

1 acre-foot is equal to 325,851 US gallons. Siberia's Lake Baikal contains about 6,276,367,740,000,000 gallons of freshwater - nearly 1 million gallons for every living person on earth.

The other - and more widely used - measure of a lake's size is the lake's surface acreage. By that measure, the world's largest freshwater lake is North America's Lake Superior.


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Maximum Depth | LakeLubbers

This is the estimated greatest depth of the water in a lake -- measured at the lake's normal elevation. The world's deepest lake is Siberia's Lake Baikal; that lake's maximum depth is estimated at 5,314 feet.

You can find many of the the world's deepest lakes on LakeLubbers. If you select the last page of that list, you will find the (maximum depth of) the shallowest lakes in our database.


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Average Depth | LakeLubbers

This is the estimated average depth of the water in a lake -- measured at the lake's normal elevation. If the water volume and surface area of a lake are known, an estimate of the lake's average depth can be calculated:

Water volume ÷ Surface Area = Average Depth

Example: 1,000,000 acre-feet ÷ 20,000 acres = 50 feet average depth


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Maximum Elevation | LakeLubbers

This is a lake's highest water level, measured by the lake's surface distance above sea level, that can occur during flooding. A lake's highest possible maximum elevation is usually the top of the lake's dam or spillway.

At lakes that include residential development, government regulations usually forbid the construction of homes below a lake's maximum elevation.


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Minimum Elevation | LakeLubbers

This is a lake's lowest water level, measured by the lake's surface distance above sea level, that can be reasonably expected to occur. Low lake levels can occur due to deliberate seasonal draw downs for irrigation or impending snow melt, reduced water inflows, drought and evaporation, residential or commercial water demands, and hydropower generation.

Some lakes' minimum and maximum elevations are virtually the same. Lakes that generate hydropower may vary by several feet - according to power demand. Lakes whose primary purpose is to prevent flooding can seasonally vary by 100 feet or more.

When some lakes reach their minimum elevation, their boat ramps may not be long enough to permit boat access - and boats docked on shallow parts of the lake may end up on dry ground. In those cases, kayakers and shore-based anglers may be among the few happy recreational users of the lake.


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Normal Elevation | LakeLubbers

This is a lake's normal water level, measured by the lake's surface distance above sea level. For a reservoir, this water level is also known as "full pond" or "full pool".

You can find many of the world's highest-elevated lakes on LakeLubbers. Lakes with the lowest elevations (known by LakeLubbers) are shown on the final page of that list.


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Shoreline Length | LakeLubbers

This is the length of the exterior shoreline around a lake - measured at the lake's normal elevation. The shoreline length can be considerably shorter or longer when lake water levels are lower or higher than normal.

A lake with many coves has a much longer shoreline than a lake of similar surface area that is nearly circular in shape.

When known, the shoreline miles that we report in our statistics include only the lake's exterior shoreline, and exclude the shorelines of islands located within a lake's boundaries. In lakes with many islands, those islands' combined shorelines may exceed a lake's exterior shoreline.

You can find many of the world's longest-shoreline lakes on Lakelubbers.


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Surface Area | LakeLubbers

This is the area (acreage, square kilometers, etc.) of the top surface area of a lake - measured at a lake's normal elevation. The surface area can be considerably smaller or larger when lake levels are lower or higher than normal. North America's Lake Superior is the world's largest freshwater lake by this measure.

The other measure of a lake's size is the lake's water volume. By that measure, the world's largest freshwater lake is Lake Baikal in Siberia.

You can find many of the world's largest lakes (acres) on Lakelubbers. There is no widely-accepted minimum surface area that defines a lake. What Lakelubbers describes as a lake, you might call a pond. The smallest lake that Lakelubbers currently includes is Hawaii's 2-acre Lake Waiau.


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Water Level Control | LakeLubbers

This is the organization that controls water releases or outflows from the lake or reservoir. In the USA, this is often the US Army Corps of Engineers, a power company, a municipal water system, an irrigation district, or a paper manufacturing company. In the case of private or gated lakes, a homeowners' association may be the lake's controlling authority.

Many lakes cross borders, including North America's Great Lakes. The control of such lakes and their coveted freshwater may be amicably shared - or hotly disputed.

"Water wars" continue at many lakes as growing populations and crop irrigation needs compete for the freshwater that lakes contain.


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Lake Type | LakeLubbers

There are 3 basic types of lakes that are currently included on LakeLubbers. 2 types may be dammed or not dammed, producing 5 classifications.

- A Reservoir is a man-made freshwater lake that is usually created by damming rivers.

- A Natural Freshwater Lake occurs naturally - often by glacial activity - and has a salinity of less than 30 parts per thousand. It may be dammed to produce electricity or for other reasons.

- A Natural Saltwater Lake occurs naturally and has a salinity of more than 30 parts per thousand (ppt). It may be dammed.

"Brackish" water may be categorized as freshwater or saltwater, depending on its salt content (salinity). Oligohaline water has less than 15 ppt of salt. Mesohaline water has 15-29 ppt. Polyhaline has 30-335 ppt.


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