World Library  
Flag as Inappropriate
Email this Article

Fish ladder

Article Id: WHEBN0000341115
Reproduction Date:

Title: Fish ladder  
Author: World Heritage Encyclopedia
Language: English
Subject: Marshall McDonald, Eel ladder, Fish counter, Abiqua Creek, Atlantic salmon
Collection: Aquatic Ecology, Dams, Ecological Connectivity, Fisheries
Publisher: World Heritage Encyclopedia

Fish ladder

Pool-and-weir fish ladder at Bonneville Dam on the Columbia River

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.[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. The velocity of water falling over the steps has to be great enough to attract the fish to the ladder, but it cannot be so great that it washes fish back downstream or exhausts them to the point of inability to continue their journey upriver.


  • History 1
  • Types 2
  • See also 3
  • Notes 4
  • References 5
  • External links 6


Denil Fishway on Salmon Creek, Montana

Written reports of rough fishways date to 17th-century France, where bundles of branches were used to create steps in steep channels to bypass obstructions. A version was patented in 1837 by Richard McFarlan of paddlefish are overloaded in the proximity of the rebar and other metal used in concrete construction, preventing them from gaining access to their spawning grounds and contributing to a catastrophic decline in their numbers.

As the Industrial Age advanced, dams and other river obstructions became larger and more common, leading to the need for effective fish by-passes.[3]


A small fish ladder on the River Otter

There are six main types of fishways:

  • Pool and weir
  • Baffle fishway (Denil, Larinier, Alaskan Steeppass, or other baffle configuration)
  • Fish elevator
  • Rock-ramp fishway
  • Vertical-slot fish passage
  • Fish siphon

A pool and weir is one of the oldest styles of fish ladders. It uses a series of small dams and pools of regular length to create a long, sloping channel for fish to travel around the obstruction. The channel acts as a fixed lock to gradually step down the water level; to head upstream, fish must jump over from box to box in the ladder.

A baffle fishway uses a series of symmetrical close-spaced baffles in a channel to redirect the flow of water, allowing fish to swim around the barrier. Baffle fishways need not have resting areas, although pools can be included to provide a resting area or to reduce the velocity of the flow. Such fishways can be built with switchbacks to minimize the space needed for their construction. Baffles come in variety of designs. The original design for a Denil fishway was developed in 1909 by a Belgian scientist, G. Denil; it has since been adjusted and adapted in many ways. The Alaskan Steeppass, for example, is a modular prefabricated Denil-fishway variant originally designed for remote areas of Alaska.

A fish elevator or fish lift, as its name implies, breaks with the ladder design by providing a sort of elevator to carry fish over a barrier. It is well suited to tall barriers. With a fish elevator, fish swim into a collection area at the base of the obstruction. When enough fish accumulate in the collection area, they are nudged into a hopper that carries them into a flume that empties into the river above the barrier.

On the Connecticut River, for example, two fish elevators lift up to 500 fish at a time, 52 feet (15.85 m), to clear the Holyoke Dam. In 2013, the elevator carried over 400,000 fish.[4]

A rock-ramp fishway uses large rocks and timbers to create pools and small falls that mimic natural structures. Because of the length of the channel needed for the ladder, such structures are most appropriate for relatively short barriers. They have a significant advantage in that they can provide fish spawning habitat.[5]

A vertical-slot fish passage is similar to a pool-and-weir system, except that each "dam" has a narrow slot in it near the channel wall. This allows fish to swim upstream without leaping over an obstacle. Vertical-slot fish passages also tend to handle reasonably well the seasonal fluctuation in water levels on each side of the barrier.

A Fish Siphon allows the pass to be installed parallel to a water course and can be used to link two watercourses. The pass utilises a syphon effect to regulate its flow. This style is particularly favoured to aid flood defence

See also

FERC Fish Ladder Safety Sign


  1. ^ "What is a Fish Ladder?". Michigan:  
  2. ^ Mario Theriault, Great Maritme Inventions 1833–1950, Goose Lane, 2001, p. 45
  3. ^ Office Of Technology Assessment Washington DC (1995) Fish passage technologies : protection at hydropower facilities Diana Publishing, ISBN 1-4289-2016-1.
  4. ^ "2013 Connecticut River Migratory Fish". United States Fish and Wildlife Service. Retrieved 8 September 2014. 
  5. ^ Luther P. Aadland (2010). Reconnecting Rivers: Natural Channel Design in Dam Removals and Fish Passage. Minnesota Department of Natural Resources. 


  • To Save the Salmon (1997) US Army Corps of Engineers.

External links

  • A study of the hydraulics of flow over fishways
  • Construction of a vertical slot fish passage and eel ladder for the St. Ours Dam (Richelieu River, Québec)
  • Fish Passage Center
  • Fish passes. Design, dimensions and monitoring, FAO's EIFAC – European Inland Fisheries Advisory Commission)
  • Washington Post, January 31, 2007: U.S. Orders Modification of Klamath River – Dams Removal May Prove More Cost-Effective for allowing the passage of Salmon
  • First "Denil" style dam in Illinois.
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.