The River Hii significantly changed its course and transformed the land several times during last 7 millennia. Alluvial deposits carried by the river joined the Shimane peninsula to the mainland, which may have been represented in the "Kunibiki-shinwa" myth. Since the 17th century it flows into lake Shinji, and since the early 20th century continues to the Sea of Japan. Hii river frequently caused floods in its catchment. On the other hand, it was and currently is an important source of drinking and irrigation water. During the Edo period the upper Hii catchment was the largest iron-producing region in Japan. Nowadays the river is dammed for the production of hydropower. The largest dams are Obara and Hinobori.
