To provide a rubble structure formed in a fish way capable of damping the momentum of a fast water flow, securing an environment in which aquatic animals such as fishes can move easily and rest, having high resistance against damage and slipping even if a torrent is caused due to floods or the like and capable of being easily restored even if the structure is damaged, enabling easy maintenance control.

An inclined waterway 2 is annexed to a crossing structure such as a weir facing a water flow in a river, and the inclination of the bottom face 3 is set to a specified value to form a pass (fishway) for aquatic animals such as fishes. The rubble structure is formed of a columnar body 1 having a cross-section of a specified shape. A large number of the columnar bodies 1 are arranged in a specified number of rows on the bottom face 3 of the inclined waterway 2. The cross-section of the columnar body 1 is flat on the upstream side, and the flat face part is disposed to face the upstream direction in the inclined waterway 2. The face of the columnar body 1 opposing the water flow does not change even if the water level rises so that the speed and momentum of the water flow can be controlled appropriately.

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