is a caldera lake in Akan National Park

Akan National Park

is a national park located on the island of Hokkaidō, Japan. Along with Daisetsuzan National Park, these are the two oldest national parks in Hokkaidō. The park was established December 4, 1934....

, eastern Hokkaidō

Hokkaido

, formerly known as Ezo, Yezo, Yeso, or Yesso, is Japan's second largest island; it is also the largest and northernmost of Japan's 47 prefectural-level subdivisions. The Tsugaru Strait separates Hokkaido from Honshu, although the two islands are connected by the underwater railway Seikan Tunnel...

, Japan

Japan

Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

. As with many geographic names in Hokkaidō, the name derives from the Ainu language

Ainu language

Ainu is one of the Ainu languages, spoken by members of the Ainu ethnic group on the northern Japanese island of Hokkaidō....

. It is the largest caldera lake in Japan in terms of surface area, and sixth largest lake in Japan. It is also the largest lake in Japan to freeze over completely in winter.

The lake’s central island, Nakajima, is a composite volcano. Volcanic gases render the lake water acidic, and it supports few fish except in areas where inflowing streams dilute the water. Rainbow trout

Rainbow trout

The rainbow trout is a species of salmonid native to tributaries of the Pacific Ocean in Asia and North America. The steelhead is a sea run rainbow trout usually returning to freshwater to spawn after 2 to 3 years at sea. In other words, rainbow trout and steelhead trout are the same species....

, which are also resistant to fairly acidic water, have been artificially introduced. In 1951, a rare form of cicada

Cicada

A cicada is an insect of the order Hemiptera, suborder Auchenorrhyncha , in the superfamily Cicadoidea, with large eyes wide apart on the head and usually transparent, well-veined wings. There are about 2,500 species of cicada around the world, and many of them remain unclassified...

 (Oncotympana maculaticollis) was discovered, and is now protected by the government. The lake is also on the migratory path of the whooper swan

Whooper Swan

The Whooper Swan , Cygnus cygnus, is a large Northern Hemisphere swan. It is the Eurasian counterpart of the North American Trumpeter Swan. An old name for the Whooper Swan is Elk; it is so called in Francis Willughby and John Ray's Ornithology of 1676.-Description:The Whooper Swan is similar in...

.

Along the lake shore are several outdoor hot springs and a sand beach with naturally heated sand and hot ground water. Wakoto Peninsula extending into the lake has a number of active sulfurous vents.

The lake is also known as Japan’s Loch Ness

Loch Ness

Loch Ness is a large, deep, freshwater loch in the Scottish Highlands extending for approximately southwest of Inverness. Its surface is above sea level. Loch Ness is best known for the alleged sightings of the cryptozoological Loch Ness Monster, also known affectionately as "Nessie"...

, after numerous reported sightings on a lake monster

Lake monster

A lake monster or loch monster is a purported form of fresh-water-dwelling megafauna appearing in mythology, rumor, or local folklore, but whose existence lacks scientific support. A well known example is the Loch Ness Monster. Lake monsters' depictions are often similar to some sea monsters...

 dubbed Kusshii

Kusshii

is the name of a Japanese lake monster said to be living in Hokkaidō's Lake Kussharo. The naming convention was likely borrowed from that of Loch Ness's Nessie....

by the press from 1973.