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What is a Fish Ladder?

Mary McMahon
Mary McMahon
Mary McMahon
Mary McMahon

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.

Raccoons congregate around fish ladders.
Raccoons congregate around fish ladders.

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.

Most dams have fish ladders, and some have turned them into wildlife viewing areas for people.
Most dams have fish ladders, and some have turned them into wildlife viewing areas for people.

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.

Frequently Asked Questions

What is a fish ladder and why are they important?

A fish ladder is a structure that allows fish to navigate around barriers like dams or weirs on their migratory routes. They are crucial for species such as salmon and trout, which migrate upstream to spawn. By providing a detour around obstacles, fish ladders help maintain fish populations and biodiversity, ensuring the survival of species that are integral to both local ecosystems and economies.

How does a fish ladder work?

Fish ladders work by mimicking natural water flows, creating a series of steps with resting pools in between. These steps are designed to accommodate the swimming ability of different fish species, allowing them to rest and navigate through the ladder at their own pace. The gradient and flow are carefully calibrated to enable fish to swim upstream without exhausting themselves.

Are fish ladders effective for all fish species?

While fish ladders are effective for many migratory species, their success can vary depending on the design and the species in question. Some fish may struggle with certain types of ladders, and not all species are inclined to use them. Research and monitoring are essential to ensure that ladders are meeting the needs of the target fish populations.

What are the different types of fish ladders?

There are several types of fish ladders, including pool-and-weir, vertical slot, and Denil fish ladders. Each type has a unique design suited to different environments and species. For example, pool-and-weir ladders are common and consist of a series of small dams and pools, while vertical slot ladders allow fish to pass through without changing direction.

Can fish ladders impact the local ecosystem?

Fish ladders can have a positive impact on local ecosystems by restoring migratory routes and supporting the life cycles of fish species. This, in turn, can benefit other wildlife that rely on fish for food. However, if not properly designed, they can also become barriers themselves or create new ecological challenges that need to be addressed.

How are fish ladders monitored for effectiveness?

Fish ladders are monitored using various methods, including video surveillance, RFID tags, and physical counts. These monitoring techniques help researchers gather data on the number and species of fish using the ladder, their success rates, and any issues they encounter. This information is vital for assessing the ladder's effectiveness and making necessary adjustments to improve functionality.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...

Discussion Comments

umbra21

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

@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

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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    • Raccoons congregate around fish ladders.
      By: Eric Isselée
      Raccoons congregate around fish ladders.
    • Most dams have fish ladders, and some have turned them into wildlife viewing areas for people.
      By: ALCE
      Most dams have fish ladders, and some have turned them into wildlife viewing areas for people.