Abstract
We surveyed and discussed the nature-oriented fishway constructed in the Oshino River in northern Gunma Prefecture, 15 years after its completion. The fishway was improved from a head construction in 1998 because high head constructions become serious obstacles for fish in migration. After the improvement, a fish release experiment was conducted using Yamame Oncorhynchus masou. The fishway had a history of receiving medium-scale or greater runoff , including runoff approaching the designed flood discharge. We surveyed the sediment deposition condition and changes in the main body 14 structure such as stones and wooden stakes, and conducted a biological survey on fish and benthic fauna, additionally taking into consideration the habitat of organisms. Sediment deposition had progressed overall in the fishway, and although some stones had washed away, the basic fishway structure and function were maintained, and we confirmed that the wooden stakes were in fair condition without rot. The presence of fish and benthic fauna was also confirmed from the results of the biological survey, and the existence of pools and dead water areas were thought to provide a diverse habitat for fish and benthic fauna.
