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Lake Mashu

Lake Mashū
摩周湖
Image-2008 Lake Masshu.jpg
View from Viewing Platform No. 1 (July 2008)
Location Teshikaga, Hokkaidō, Japan
Coordinates 43°35′N 144°31′E / 43.583°N 144.517°E / 43.583; 144.517Coordinates: 43°35′N 144°31′E / 43.583°N 144.517°E / 43.583; 144.517
Type crater lake, endorheic
Primary inflows two streams
Primary outflows seepage
Catchment area 32.4 km2 (12.5 sq mi)
Basin countries Japan
Max. width 6 km (3.7 mi)
Surface area 19 km2 (4,700 acres)
Average depth 137.5 m (451 ft)
Max. depth 211.5 m (694 ft)
Water volume 2.86 km3 (0.69 cu mi)
Shore length1 19.8 km (12.3 mi)
Surface elevation 351 m (1,152 ft)
Frozen December to April
Islands Kamuishu Island
Settlements none
1 Shore length is not a well-defined measure.

Lake Mashū (摩周湖 Mashū-ko?) (Ainu: Kamuy-to) is a 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.

Lake Mashū is surrounded by steep crater walls 200 metres (660 ft) high. It has no significant inlets and no outlet. The lake is one of the clearest in the world and one of the deepest in Japan. On August 1, 1931 the transparency of the water was measured at 41.6 metres (136 ft). Lake Baikal was measured around the same time measured 40.5 metres (133 ft). This is the lake's claim to clearest in the world. Since the 1950s the transparency has tended to range between 20 and 30 metres (66 and 98 ft). The loss in transparency is probably due to the introduction of sockeye salmon and rainbow trout into the lake and landslides. At the same time, the clarity of Lake Baikal has not been measured.

In summer, the surface of Lake Mashū is often obscured by fog. This has given the lake a reputation for mysteriousness.A local legend says that if you can see the surface of the lake, you will have bad luck.

Lake Mashū was originally named Lake of the Devil by the Ainu. This was rendered as Lake Mashin (魔神湖 Mashin-ko?) by the Japanese. Over time, however, the Japanese began to refer to the lake by the Japanese reading for the neighboring peak, Mount Mashū (摩周岳 Mashū-dake?). The kanji for this peak translate roughly as scrubbed area mountain. The Ainu name for this peak, by which it is commonly known today, is Kamuinupuri or mountain of the gods. The lake also retains its Ainu name, Kamuito or lake of the gods.


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