Frozen Lake Mashu

Frozen Lake Mashu

KUSHIRO, Japan - Photo taken Feb. 26, 2013, shows Lake Mashu in Teshikaga, Hokkaido, the entire surface of which has frozen.

Frozen Lake Mashu

Frozen Lake Mashu

TESHIKAGA, Japan - Photo taken Feb. 28, 2012, shows frozen Lake Mashu in Teshikaga, Hokkaido.

Excursion ship Mashu Maru breaks ice on Lake Akan

Excursion ship Mashu Maru breaks ice on Lake Akan

Sightseeing cruiser Mashu Maru breaks the ice on Lake Akan in Kushiro in Japan's northernmost prefecture of Hokkaido on April 16, 2015, to forge a course ahead of the start of its full-fledged operation in May. (Kyodo) ==Kyodo

Excursion ship Mashu Maru breaks ice on Lake Akan

Excursion ship Mashu Maru breaks ice on Lake Akan

Sightseeing cruiser Mashu Maru breaks the ice on Lake Akan in Kushiro in Japan's northernmost prefecture of Hokkaido on April 16, 2015, to forge a course ahead of the start of its full-fledged operation in May. (Kyodo) ==Kyodo

Frozen Lake Mashu

Frozen Lake Mashu

TESHIKAGA, Japan - Photo taken Feb. 28, 2012, shows frozen Lake Mashu in Teshikaga, Hokkaido. (Kyodo)

Sightseeing boat on icy Lake Akan in Hokkaido

Sightseeing boat on icy Lake Akan in Hokkaido

The Mashu Maru excursion boat breaks the ice on Lake Akan in Kushiro on Japan's northernmost main island of Hokkaido on April 17, 2019. (Kyodo) ==Kyodo

Sightseeing boat on icy Lake Akan in Hokkaido

Sightseeing boat on icy Lake Akan in Hokkaido

The Mashu Maru excursion boat breaks the ice on Lake Akan in Kushiro on Japan's northernmost main island of Hokkaido on April 17, 2019. (Kyodo) ==Kyodo

Sightseeing boat breaks ice on Lake Akan in Hokkaido

Sightseeing boat breaks ice on Lake Akan in Hokkaido

The Mashu Maru excursion boat breaks the ice on Lake Akan in Kushiro in Japan's northernmost main island of Hokkaido on April 16, 2018, ahead of the start of the sight-seeing season in May in the lake, which is known for its rare "marimo" green algae balls. (Kyodo) ==Kyodo

Sightseeing boat breaks ice on Lake Akan in Hokkaido

Sightseeing boat breaks ice on Lake Akan in Hokkaido

The Mashu Maru excursion boat breaks the ice on Lake Akan in Kushiro in Japan's northernmost main island of Hokkaido on April 16, 2018, ahead of the start of the sight-seeing season in May in the lake, which is known for its rare "marimo" green algae balls. (Kyodo) ==Kyodo

Sightseeing boat Mashu Maru breaks ice on Lake Akan

Sightseeing boat Mashu Maru breaks ice on Lake Akan

The sightseeing boat Mashu Maru breaks the ice on Lake Akan, with Mt. Oakan in the background, in Kushiro on Japan's northernmost main island of Hokkaido on April 17, 2017, before resuming business in May. The lake is known for its rare marimo green algae balls. (Kyodo) ==Kyodo

Sightseeing boat Mashu Maru breaks ice on Lake Akan

Sightseeing boat Mashu Maru breaks ice on Lake Akan

The sightseeing boat Mashu Maru breaks the ice on Lake Akan, with Mt. Oakan in the background, in Kushiro on Japan's northernmost main island of Hokkaido on April 17, 2017, before resuming business in May. The lake is known for its rare marimo green algae balls. (Kyodo) ==Kyodo