Lake Mashū 摩周湖
In 1930 its transparency reached 41.6 m, surpassing Baikal; in 2015 it measured only 17.2.
Lake Mashū fills the caldera of the Mashū volcano, in Kawakami District, and has no inflowing or outflowing streams visible on the surface: water comes in from rain and groundwater and drains away underground. Its transparency reached the world record of 41.6 metres in August 1930, beating Lake Baikal (40.5 m, measured in 1911); it had already fallen to 29 metres by 1952, for a reason the sources do not explain, and in 2015 it stood at 17.2 metres. The 1966 song ‘Kiri no Mashū-ko’ spread its fame as a place wrapped in fog.
Hokkaido
Mashuko Dai-ichi Tenbodai (摩周湖第１展望台)
