Lake Koyama

A lagoon in the northeastern part of Tottori Prefecture, west of the city of Tottori. It has a shoreline of about 17 km, an area of ​​6.9 km2, and an average depth of 2.8 m, with a maximum depth of 7 m in the northern part, which is getting shallower every year. It is said to have been formed when the ancient Tottori Sea, which was formed during the postglacial period of slight sea level highs, was left behind by the siltation of the Sendai River during the subsequent sea level drop, and the development of the Koyama sand dunes. There are five rare islands in the lake that give the impression of islands in the sea. It is a eutrophic lake, and in recent years the amount of salt has increased due to the inflow of seawater, and the amount of nitrogen and phosphorus has increased due to the inflow of domestic wastewater and fertilizer. In the fall, the multiplying eels are deposited and rot, generating hydrogen sulfide. It is rich in freshwater fish such as carp, crucian carp, cattle egrets, and eels, and is characterized by cold-weather fishing using artificial fish reefs made of rocks called "ishi-gama." There is a legend about a rich man who invited the setting sun back and finished planting rice, and so his rice field turned into a lake overnight.

[Minoru Iwanaga]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

鳥取県北東部、鳥取市街地西郊の潟湖(せきこ)。湖岸線延長約17キロメートル、面積6.9平方キロメートル、平均水深2.8メートル、最深部は北部の7メートルで年々浅化している。成因は後氷期の微高海面期にできた古鳥取海が、その後の海面低下期に進んだ千代(せんだい)川の埋積作用や湖山砂丘の発達により埋め残されたものといい、潟湖には珍しい湖中の5島があって海島のおもかげを残す。富栄養湖で最近は海水の流入による塩分や生活汚水、肥料の流入による窒素、リンなどが増え、秋には増殖したアイモが沈積腐敗して硫化水素が発生する。コイ、フナ、アマサギ、ウナギなどの淡水魚に富み、「石がま」とよぶ岩組みの人工魚礁による寒中漁労が特色である。夕日を招き返して田植を終えたため、水田が一夜で湖となったという長者伝説がある。

［岩永　實］

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