In Niigata Pref., there are two famous ponds which have floating islands formed of waterweeds, Uki Shima. One is Otowa Ike in Sado Island and the other is Kooridono No Ike in Ojiya City. Strangely, folk tales of each pond tell about a girl and a dragon god, Ryu Jin. In Kooridono No Ike, microscopic creatures called diatoms live and their characteristics are different from other diatoms (A. Kuriyama and S. Mayama: 17^th International Diatom Symposium.). Kooridono No Ike is designated as Natural Monument by Ojiya City.

参考：小千谷市ホームページ

２０１４．１．１８