To insure and protect the living territory of aquatic organism by providing this protector in a waterway, so that the aquatic organism can live even in a waterway, a river, and the like of which the floor faces and wall faces are hardened by concrete.

A bent part 1a is provided on the upper edge of a plate, and supporting pins 2 are fitted to a little lower part of it. The supporting pin 2 is projected on the back side of the plate 1, so as to make the plate 1 in slanting state. A flexible sheet 3 is stuck to the lower end part 1b of the plate 1. The flexible sheet 3 is extended in front of the plate 1, and also extended sideway so as to provided projecting parts 3c. The fitting side of the flexible sheet 3 is installed so as to face to the upper stream of a waterway. Hereby, it does not move on the floor face of the waterway and it is stabilized. The living space for aquatic organism is insured on the back side of the plate 1.