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What is a Fish Ladder?

Raccoons congregate around fish ladders.
Most dams have fish ladders, and some have turned them into wildlife viewing areas for people.
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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 11 December 2014
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A fish ladder is a structure which allows fish to move past an obstacle such as a dam. Without fish ladders, fish would be stuck downstream of the obstacle, and this could potentially have a negative impact on the breeding cycles and lifestyle of the fish. Many dams are equipped with fish ladders, often to satisfy requirements from government agencies, and some dams have turned their fish ladders into wildlife viewing areas, allowing visitors to watch the fish as they move up the ladder.

The term “ladder” might seem a bit confusing for people who are trying to figure out how fish could climb up a conventional ladder. Fish ladders are actually made by creating a series of stepped pools. The fish can jump from pool to pool, eventually coming out on the other side of the dam or obstacle. There are a number of different designs and configurations for the pools. For especially large dams, people may use a fish elevator instead. Just like a people elevator, a fish elevator fills with passengers and then rises to the top of the dam before opening to allow the fish out on the other side.

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Depending on where one is, fish ladders may be referred to as fishways, fish passes, or fish steps. They are usually designed in such a way that the water becomes noisy, attracting the attention of fish who may be struggling at the foot of a dam. The water is kept calm enough for the fish to be able to swim in the pools, as the designers of fish ladders do not want the fish to get so tired that they cannot navigate the fish ladder successfully.

In some cases, the fish ladder may be mounted in a glass chamber on the side of the dam, allowing observers to watch the fish as they move up the ladder. This can be useful for biologists who want to study the movement of fish populations and look at how dams are impacting fish in a particular region. Visitors to the dam may also enjoy watching the fish as they leap from pool to pool, or hop down the fish ladder, depending on the time of year and the species.

Local wildlife also may become interested in fish ladders, since the ladder confines the fish in a narrow inlet, making it easy to swoop in and grab a snack. Bears, eagles, raccoons, and other fish-eaters tend to congregate around fish ladders, regarding them as a movable feast of fish species.

People have recognized the impact of dams on fish since at least the 1600s, when fish ladders first began to be constructed. Modern versions differ little from the fish ladders of the 18th and 19th century, illustrating the soundness of the basic fish ladder design.

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umbra21
Post 3

I'd love to go and see one of these salmon fish ladders. I always think of fish as being relatively quiet animals, but they must be really strong to be able to leap from pool to pool like that. It must be an amazing sight, and it would be really cool to see the bears and things that gather around to eat them as well.

Mor
Post 2

@Iluviaporos - Unfortunately, it's not only the fish that suffer. Spawning salmon, in particular, are often a huge part of the food chain in an ecosystem, at many different levels. I read about an experiment once where they basically shipped in salmon carcasses and left them where they would have died at the top of a river if the river still had spawning salmon.

The plants and little animals of the places with the carcasses increased by a huge amount compared to the ones that didn't have them, basically because of all the extra nutrients that were put into the ecosystems there.

That's not even getting into the predators that eat fish and the prey that should be eaten by the fish. We probably don't even realize the damage that has been done. I just wish it had always been mandatory to have a fish ladder put into a dam whenever one was built.

lluviaporos
Post 1

There are some pretty cool documentaries on fish ladders and what happens when a dam is built without them. I saw one recently which talked about how many of the rivers in North America used to be swarming with salmon but are now basically empty because of dams that were put in.

If they had put in a fish passage while they were building the dam, there wouldn't have been a problem, but now there's nothing to be done unless they can figure out a good way to introduce the salmon back into the rivers (which is difficult for many reasons).

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