When the river 42 cross-section such as a beam 11 or a dam is constructed in the river 42, the flow of water is blocked and the movement of the fish 12 is prevented, thereby destroying the river ecosystem.;The esophagus 10 is a structure that functions as a small passage for the migratory fish 12 such as sweetfish, salmon, eel, and yellowfish in a spawning season, and the local migratory fish 12 such as pyramids, sharks, and eel. The fish (12) provides a way to fish in the cross-section to freely travel to prevent the destruction of the river ecosystem.;The present invention is to install the transparent window 32 on the side wall or fish habitat 50 of the structure (10), and the bend observation mirror 30 of the periscope principle tightly connected to the transparent window 32 to install the river (42) In the green space of the blunt 41, it is possible to easily observe the small-scene scene and the habitat scene of the fish 12 during the walk.;Edo, Little Statue, Periscope
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