1) Structure for spawning salmon 
A fish ladder, also known as a fishway, fish pass or fish steps, is a structure on or around artificial and natural barriers (such as dams, locks and waterfalls) to facilitate diadromous fishes` natural migration. Most fishways enable fish to pass around the barriers by swimming and leaping up a series of relatively low steps (hence the term ladd....
A series of interconnected pools created up the side of a river obstruction, such as a weir, to allow salmon and other fish to pass upstream.
(from the article `dam`) Fish passes usually take the form of fish ladders and fish locks. A fish ladder is utilized at Pitlochry Dam in Scotland; it consists of a series of ...
A series of descending weirs which carry water around a dam or waterfall to facilitate the upstream migration of fish. ... (09 Oct 1997) ... 
See Fishway.
a series of pools arranged like steps that fish (salmon or trout) use to move upstream over a dam
[n] - a series of ascending pools providing a passage for salmon to swim upstream past a dam
noun a series of ascending pools providing a passage for salmon to swim upstream past a dam
a man-made series of pools at the side of a stream arranged like ascending steps, enabling migrating fish to swim upstream around a dam or other obstruction
a series of interconnected pools created up the side of a river obstruction, such as a weir, to allow salmon and other fish to pass upstream.
a series of ascending pools constructed to enable salmon or other fish to swim upstream around or over a dam.