is a near circular caldera

Caldera

A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...

 lake in Shiraoi

Shiraoi, Hokkaido

is a town located in Shiraoi District, Iburi, Hokkaidō, Japan. As of 31 May 2008, the town had a population of 20,371 The town was established in 1867 by the feudal lords of Sendai. Most of the area of the town is forested and parts lie within the Shikotsu-Tōya National Park.-History:Shiraoi like...

, 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...

. It is part of Shikotsu-Tōya National Park

Shikotsu-Toya National Park

is a national park in the central part of the island of Hokkaidō, Japan. Named after the volcanic caldera lakes of Lake Shikotsu and Lake Tōya, it has a total area of 993.02 square kilometers...

. The lake is recognized as having the best water quality in all of Japan. With a transparency of 19 metres (62.3 ft), the lake ranks second only to Lake Mashū

Lake Mashu

is a landlocked endorheic crater lake formed in the caldera of a potentially active volcano. It is located in Akan National Park on the island of Hokkaidō, Japan. The lake has been called the clearest lake in the world.-Hydrology:...

 according to the Ministry of the Environment

Ministry of the Environment (Japan)

The ' of Japan was formed in 2001 from the sub-cabinet level Environmental Agency established in 1971. The minister is a member of the Cabinet and is chosen by the Prime Minister, usually from the Diet., the current is Goshi Hosono...

.

Resident species of the lake include a salamander

Salamander

Salamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...

 species, . Since 1909 Sockeye salmon

Sockeye salmon

Sockeye salmon , also called red salmon or blueback salmon in the USA, is an anadromous species of salmon found in the Northern Pacific Ocean and rivers discharging into it...

have been introduced to the lake.