geo.wikisort.org - Reservoir

Ōike (大池) is a karst pond on Minamidaitōjima, Okinawa Prefecture, Japan. Ōike is the largest pond containing both freshwater and seawater.^{[clarification needed]} It covers 0.31 square kilometres (0.12 sq mi), the circumference is 5.50 kilometres (3.42 mi), and it is 1.3 metres (4 ft 3 in) at its deepest point. Fresh water is mixed with seawater beneath.

Ōike
Ōike
Location	Minamidaitōjima, Okinawa Prefecture, Japan
Coordinates	25°51′18″N 131°14′19″E
Native name	大池  (Japanese)
Surface area	0.31 km2 (0.12 sq mi)
Max. depth	1.3 m (4 ft 3 in)
Shore length1	5.50 km (3.42 mi)
1 Shore length is not a well-defined measure.

Geology

The island is composed of elevated limestone from its atoll.^{[citation needed]} Rainwater has dissolved the limestone leading to a depression in the ground (sinkhole). This has filled with water to become a pond.^{[citation needed]}

Natural history

On the north of the pond extends an area of wetland with large communities of Bruguera gymnorrhiza, a mangrove plant, which was designated as a Natural monument since it is unique in freshwater on March 18, 1975.^{[citation needed]} Other plants include Scirpus tabemaemontani C. C. Gemlin, Panicum repens L. Najas marina and Vallisneria natans.^{[citation needed][clarification needed]}

Common carp and Carassius auratus langsdorfii were introduced in 1910 and tilapia in 1955.^{[citation needed]} Birds include mallard, Pacific reef heron, common moorhen and cattle egret.[1]

Footnotes

References

• Ministry of the Environment, Environment of lakes and ponds in Japan part 2 1995, Nature and Environment Research Center, ISBN 4-915959-10-4
• Masaaki Tanaka, Lakes and ponds in Japan 2 2004, University of Nagoya Press, ISBN 4-8158-0492-3

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