Lake Oze ASI-41

Riparian Nation(s) Japan
Surface Area 2 km2 Mean Depth 4.1 m Volume 0.0066 km3
Shoreline 6 km Catchment Area 13.4 km2 Residence Time 0.28 yr
Frozen Period Dec-May Mixing Type Dimictic Morphogenesis/Dam Volcanic
Related Info/Site Oze National Park (1924), Wildlife Reserve Area (1953), Ramsar Site #1554 (2005)


The Oze district is a wilderness area composed of Lake Oze or Oze-numa and Ozegahara moorland. Oze-numa is a small montane lake with a total shoreline length of about 7 km and a surface area of 1.7 km2. It is located at an altitude of 1,665 m across the prefectural boundary between Fukushima and Gunma, while Ozegahara moor extends over the three prefectures, Fukushima, Gunma and Niigata. The entire Oze area was designated as the 4th National Park of Japan in 1924, the 12th Wildlife Reserve Area in 1953, and a Special Natural Monument in 1960, based on the Cultural Properties Protection Law.

Some eleven thousand years ago, the eruption of Mt. Hiuchi, a volcano to the NE of the present lake, emitted a vast amount of ejecta eastward blocking the Tadami River to form a lake called Old Ozegahara Lake, which has since been filled up and turned into Ozegahara moor. The present Oze-numa was produced later toward the end of the volcanic activity by the southward lava flow that blocked the Numajiri River. The lake is believed to have been much deeper originally, but sediment loads eroded from Mt. Hiuchi made it shallower and produced an extensive marshy area around the lake.

The Oze area is one of the cores of , and is known as the symbol of nature protection movement in Japan. It is blessed with fascinating natural beauty and is called the treasure box of mountain flora. Over nine million tourists visit this area annually, particularly during the blooming season of wild plants. However, the increase of visitors due to improved transportation in recent years, together with the wastewater discharge from tourist lodges and the invasion of an exotic waterweed Elodea canadensis into the lake, has resulted in the progressive disruption of pristine environments to a serious extent (Q1, Q2).

Photo of Lake Oze
Photo: Fukushima Prefectural Government