Migratory fish and dams: Going beyond the classroom at Cabin John Middle School Part II

Image of the Simkins Dam by NOAA
February 26, 2014

The students at Cabin John Middle School don’t just learn about their environment — they take active steps to help make it a better place!


Migratory Fish: The Challenge of Passage Over Dams

Project and Presentation by: Neema Aalemansour, William Ahn, Martin Li, Margaret Tilmes, Claire Yang

Our environmental issue focused on dams, the impact of dams on migratory fish, and ways to help migratory fish pass over dams. First, we had to understand dams. We found that dams have pros and cons.

Image of Cabin John Middle School students presenting their research at a community event.


  • They can be very useful, providing hydropower and other economic benefits, including jobs;
  • offering flood control and irrigation; and
  • preventing invasive species from moving further up rivers.

But, on the other hand…


  • Dams negatively affect all fish by altering important abiotic factors like the river’s flow, water temperature, sediment levels and nutrient distribution.
  • Dams also alter many biotic factors including diminishing plant, amphibian and other wildlife along riparian banks. These changes stress all types of fish, making it hard for them to reproduce, so fish populations are declining all over the country.
  • Migratory fish are hardest hit, because dams block their ability to reach spawning grounds. The problem is well known and many efforts are being made to help migratory fish pass dams. Yet, despite these efforts, once abundant migratory fish populations are collapsing.


Image of Cabin John Middle School students presenting on their migratory fish and dam research

Our Project

We followed several steps to complete this project: conducting research; building a model; making a display board; creating a power point presentation; and finally, making a public presentation to raise awareness.  In order to educate the public and raise awareness about the effect of dams on migratory fish, we decided to build a model.

After our model was built, we created a display board to show real world examples of dams, the various types of fish passage, the number of miles of fish passage that has been opened up in the Chesapeake Bay and dam removals. Then, we developed a power point presentation following a scientific rubric set out by our teacher, Mr. Elmer. Finally, we made a public presentation at the Croyden Creek Nature Center.


What We Learned

We learned about dams, the special nature of anadromous (migratory) fish, the impact of dams on them, different strategies to help them pass over dams, the limits of fish passage and when dam removal works best.

First, we were very surprised to learn that most rivers in the U.S. are blocked. In fact, the U.S. Fish and Wildlife Service estimates there are 2.5 million blockages on our rivers! Most of these dams are very old and have no more economic value. Still, some are very important economically.


Image of American Shad

American Shad (Photo by South Carolina DNR)


Second, we found out the anadromous fish commonly found in the Chesapeake Bay area are American Shad, Hickory Shad, American Eel, Blue-Back Herring, Striped Bass, and Alewives. These fish are considered migratory fish because they are born in fresh water rivers and live most of their lives in saltwater oceans but eventually return to fresh water rivers to spawn.

Third, many fish passages have been built over the last decade. In the Chesapeake watershed, more than 2,500 miles of fish passages have been opened since 1989. There are several different types of fish passes – ladders, lifts, locks and natural passage — that can be built depending on the height of the dam, the types of fish that need to pass the dam and the budget available for building the pass. Some details:

Graphic of a fish ladder

Fish Ladder (Graphic By NOAA)


  • Fish ladders, where fish swim into a small entrance to access the ladder on the river. Once they have entered, fish swim against the current to move up the ladder. After ascending up to 10 feet, fish turn and rest in pools before moving to the next ascent. There are several different kinds of fish ladders. The most common fish ladder in Maryland is the denil ladder. It is built with concrete and has closely spaced baffles to control the speed of water flowing down. Fish ladders cost the least to build but require some maintenance to keep them free of debris, especially leaves and branches. Depending on the river, only 10-50 percent of fish successfully survive passage.
  • A fish lift is basically an elevator for fish. Like a ladder, fish must first find a small entrance (on a dam that can be several thousand feet wide), swim into a container at the base of the dam, and then be lifted over the dam. Lifts can help far more fish pass than ladders but some fish like American shad, herring and alewife have a hard time surviving because the lift clumps big fish together with smaller fish in a tight container with little water before pushing the fish out forcefully into the water. Lifts are expensive to build and maintain; they are usually only built on large, commercial hydropower plants.
  • A fish lock works like a canal for fish. The upper gates are closed, and then the lower gates open for fish to swim in from the river. After that the lower gates close and the upper gates open, filling the lock to the level of reservoir so fish can swim into reservoir easily. The fish lock is very easy for fish to get into and it is not stressful for them to float out to the reservoir either. But locks have not been very successful at helping large numbers of migratory fish pass because fish don’t always stay in the lock until the gate closes and they don’t always swim out when it opens. Adding a current to help the fish orient and move has helped!
  • A natural fish passage is a river-like bypass carved into land on the banks of a dammed river. It is built with mostly natural materials such as rocks, logs, and gravel. This means that fish can pass the dam naturally. The bypass lets many kinds of fish move up and downriver naturally through all stages of life cycle, helping to promote survival of a variety of fish. This is the most expensive type of fish passage to build but it is also the most successful of all the man-made fish passages: more than seventy percent of fish make it past dams!
Image of a fish lift in use in South Carolina

Fish Lock (Graphic By South Carolina DNR)


What Works and Doesn’t Work

But, after more than a decade of building fish passages, there is growing evidence that fish passage just doesn’t work as well as everyone had hoped it would. Partly, it’s the fish: a lot of fish are very finicky; some will only go into a fish ladder if it is on the right bank or vice versa. Others will not continue up a ladder if the turn into the resting pool is too sharp.

Partly, it’s the passages themselves: lifts and locks can have mechanical difficulties in the height of the short spawning season so not many fish pass. In the end, less than half the fish make it through ladders lifts and locks. On a river with many dams, like the Susquehanna, less than half of the fish pass each dam so in the end less than five percent of the migratory fish ever make past the fourth dam (York Haven Dam) to reach traditional spawning grounds; fewer still make it back down the river to the ocean to grow up! So, fish populations continue to decline.

As a result, there is growing support for dam removal in order to restore natural habitats for fish so fish populations can recover. Dam removal is often best for fish because it restores the natural habitat so all species (big and small) can pass, there is no maintenance needed, and it is a self-sustaining ecosystem. Even one dam removal can open a large watershed with thousands of stream miles.


Image of the Simkins Dam

Simkins Dam (Photo by NOAA)


Still, removing dams isn’t always the best option either. We have to accept that we will always need some dams for economic reasons and that some dams should never be removed because they hold back polluted sediments or invasive species. When we need to keep a dam, a priority should be placed on installing natural fish passages. Building multiple entrances on both sides of the river so fish have a better chance of finding the lifts and ladders would be another way to upgrade fish passages.

Overall, we discovered that we have to be really careful about how we impact the environment; the environmental issues involving dams are much bigger and more complex than many realize. Dams affect not just fish, plants, frogs, birds, and other animals but they also affect humans. When fish stocks begin to decline, whole ecosystems, including those we depend on, begin to collapse.



We hope many benefited as a result of our project. We hope the public became more educated by our presentation on dams and their effects on migratory fish in the Chesapeake Bay watershed. We also hope we made a difference by helping to build support for individual, non-profit, and government efforts to help save migratory fish. We are very grateful to the Croyden Creek Nature Center because they gave us the opportunity to present our model and findings publicly.

Our group also really benefited from this project. We feel very proud because we were able to organize ourselves outside and get a lot done outside of school. We worked together over several months to build an awesome working model; it was a lot of work but we also had a lot of fun! We also really benefited from learning how to create a power point presentation and then actually present it publicly. Once we understood the importance of this issue, we really enjoyed sharing what we had learned.

In the end, we came up with several ideas about how we all can contribute to solving this problem in addition to identifying steps dam operators and government officials can take.

  • Our short-term solution to this huge problem was to educate the community in order to raise public awareness about dams and their effect on migratory fish. We recommended that people could help by going green at home. Reducing chemical use at home and being more careful when we garden to reduce sediment run-off into our rivers and the Chesapeake Bay is very important.
  • We also educated the public about the positive impact of upgraded fish passage at economically important dams, giving priority to natural fish passage at large dams, and supporting dam removal as much as possible. We hope a more educated public will support these kinds of initiatives.
  • Finally, we wrote a letter to the Department of Natural Resources to share what we had learned; inform the Department about our concern for American Shad and other collapsing fish populations in the Chesapeake Bay watershed; and, state our hope that a natural fish passage could be built at the Conowingo Dam before it is relicensed this year.


This is the second in a three-part series on some of the projects performed by the 6th grade class of Investigations in Science.  View Part I: Going Green Action Plan.  As part of their fall semester project, groups of 6th grade students performed environmental research and community service projects on topics such as invasive plants, fish migration and dams and wildlife conservation.


2 comments on "Migratory fish and dams: Going beyond the classroom at Cabin John Middle School Part II"

  1. Unknown says:

    This is awesome! You guys did great. I love your idea of the project.

  2. Aaron says:

    That is awesome!

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