To disperse an overflow stream while preventing breakage of fins and prevent vibration of a bag-shaped body by providing netlike fins having one or more openings of a specified size at the nearby position of the top of the rubber bag-shaped body constituting a rubber weir.

A rubber-made bag-shaped body 1 constituting a rubber weir is fixed to a river bed by using fixing metal fixtures 2. One or more netlike fins 4 having openings of 1-10 cm in one side thereof are formed at the top of the rubber-made bag-shaped body 1. Since the netlike fin 4 randomizes the overflow water stream of the rubber weir and lessens a negative pressure between the rubber-made bag-shaped body 1 and the overflow water, the vibration of the rubber weir can be reduced. Further, colliding impulses of the overflow water against the fins 4 can be absorbed and secondary vibration and noise can be remarkably reduced.