Lake Mashu

About Lake Mashu

A lake in the Mashu caldera, formed by an eruption about 7,600 years ago; Kamuishu Island in the lake is a volcano that grew after the caldera formed. In 1931 it recorded a transparency of 41.6 m, and its color is called Mashu Blue. Frequent fog gives it the name Lake Mashu of the Mist, and it is also called Kamuito, the lake of the gods. In the 1991 survey its transparency of 28.0 m was still the highest in Japan, and it had the longest shoreline of any unmodified lake.

Sources: Japan Meteorological Agency, Caldera volcanoes (National Catalogue of the Active Volcanoes in Japan), Ministry of the Environment, Akan-Mashu National Park: Highlights, Environment Agency of Japan, Lake Survey Report (1993) (sources in Japanese)

Lake data

Area

19.22 km²#9 in Hokkaido

Maximum depth

211.4 m#2 in Hokkaido

Average depth

137.5 m

Surface elevation

351.3 m

Transparency

28 m#1 in Hokkaidoas of the 1991 survey

Origin

Caldera lake

Lake type

Oligotrophic

Fresh or brackish

Freshwater

Freezing

Freezes in winter

Unmodified lake

Yes (shore entirely natural)

Natural park

Akan-Mashu National Park

Lake number

0450number in the national lake survey

Sources: Geospatial Information Authority of Japan, Area Statistics of Prefectures and Municipalities 2026 (as of July 1), Geospatial Information Authority of Japan, Lake Survey (surveyed 1986), Environment Agency of Japan, 4th National Survey on the Natural Environment: Lake Survey Report (1993). Area and depth use newer figures from the Geospatial Information Authority of Japan where available. Origin, lake type, transparency, freezing and unmodified status are as of the 1991 survey.

Themes that include Lake Mashu

• Caldera lakes
• Oligotrophic lakes
• Freshwater lakes
• Unmodified lakes