fish ladder (plural fish ladders)
- A structure built on or around dams or locks to faciliate the migration of fish.
- 1941, Emily Carr, Klee Wyck, Chapter 18, 
- We came to the base of an abnormally long perpendicular fish ladder, stretching up, up into shadow so overwhelmingly deep it seemed as if a pit had been inverted over our heads.
structure to facilitate migration of fish