Fish ladder

[1] Most fishways enable fish to pass around the barriers by swimming and leaping up a series of relatively low steps (hence the term ladder) into the waters on the other side.

Written reports of rough fishways date to 17th-century France, where bundles of branches were used to make steps in steep channels to bypass obstructions.

[2] A pool and weir salmon ladder was built around 1830 by James Smith, a Scottish engineer on the River Teith, near Deanston, Perthshire in Scotland.

[3] A version was patented in 1837 by Richard McFarlan of Bathurst, New Brunswick, Canada, who designed a fishway to bypass a dam at his water-powered lumber mill.

While the culvert discharge capacity derives from hydrological and hydraulic engineering considerations,[25] this results often in large velocities in the barrel, which may prevent fish from passing through.

It is believed that fish-turbulence interplay may facilitate upstream migration, albeit an optimum design must be based upon a careful characterisation of both hydrodynamics and fish kinematics.

[24][30][31] Finally the practical engineering design implications cannot be ignored, while a solid understanding of turbulence typology is a basic requirement to any successful boundary treatment conducive of upstream fish passage.

Pool-and-weir fish ladder at Bonneville Dam on the Columbia River
Drone video of a fish way in Estonia, on the river Jägala
FERC fish ladder safety sign
Denil Fishway on Salmon Creek, Montana
This fish failed to enter the narrow opening in the fish ladder in Akerselva , Norway