In Sendai River system in Tottori Prefecture, 33 weirs have been obstacle to upstream migration of Ayu fish. The Eino weir is one of the most important places for the migration. At the immediately downstream of the weir, a lot of Ayu fish have been stagnated outside the entrance of permanent fishway, and this might be caused by the position of the fishway and the existence of the flow passing over weir. The same situation has occurred at around half of the obstacle points. In this study, the authors proposed a new portable fishway that is installed parallel to the weir axis in order to adjust the position and the slope of the fishway easily. The field observation confirmed that the installation of the fishway enabled the upstream migration of Ayu fish stagnated at the immediately downstream of the weir. Flow characteristics in the fishway were made clear. Also, the total number of the days when Ayu fish could migrate through the fishway was predicted by hydrological approach.
