"Salmon ladder" (visual definition)

Cf. verbal definitions e.g. "a series of steps in a river designed to enable salmon to bypass a dam and move upstream to their breeding grounds".
https://www.thefreedictionary.com/salmon+ladder

Rules for fishing salmon in the river Akerselva in Oslo (I haven't tried): https://www.ofa.no/fishing-rules/fishing-in-akerselva/