How Fish Survive Hydro Turbines

Most of the largest dams in the US were built  before we really understood the impacts they would  

have on river ecosystems. Or at least they were  built before we were conscientious enough to weigh  

those impacts against the benefits of a dam. And,  to be fair, it’s hard to overstate those benefits:  

flood control, agriculture, water supply for  cities, and hydroelectric power. All of our  

lives benefit in some way from this enormous  control over Earth’s freshwater resources.

But those benefits come at a cost, and the  price isn’t just the dollars we’ve spent on  

the infrastructure but also the impacts dams have  on the environment. So you have these two vastly  

important resources: the control of water to the  benefit of humanity and aquatic ecosystems that we  

rely on, and in many ways these two are in direct  competition with each other. But even though most  

of these big dams were built decades ago, the ways  we manage that struggle are constantly evolving as  

the science and engineering improve. This is  a controversial issue with perspectives that  

run the gamut. And I don’t think there’s one right  answer, but I do know that an informed opinion is  

better than an oblivious one. So, I wanted to see  for myself how we strike a balance between a dam’s  

benefits and environmental impacts, and how that’s  changing over time. So, I partnered up with the  

folks at the Pacific Northwest National Laboratory  (or PNNL) in Washington state to learn more. Just  

to be clear, they didn’t sponsor this video and  had no control over its contents.They showed me  

so much, not just the incredible technology and  research that goes on in their lab, but also how  

it is put into practice in real infrastructure  in the field, all so I could share it with you.  

This is McNary Dam, a nearly  1.5-mile-long hydroelectric dam  

across the Columbia River between  Oregon and Washington state,  

just shy of 300 miles (or 470 km) upriver from  the Pacific Ocean. And this is Tim Roberts,  

the dam’s Operations Project Manager and  the best dam tour guide I’ve ever met.

But this was not just a little walkthrough. We  went deep into every part of this facility to  

really understand how it works. McNary is one  of the hydropower workhorses in the Columbia  

River system, a network of dams that provide  electricity, irrigation water, flood control,  

and navigation to the region. It’s equipped with  fourteen power-generating turbines, and these  

behemoths can generate nearly a gigawatt of power  combined! That means this single facility can,  

very generally, power more than half-a-million  homes. The powerhouse where those turbines live  

is nearly a quarter mile long (more than 350  meters)! It’s pretty hard to convey the scale  

of these units in a video, but Tim was gracious  enough to take us down inside one to see and  

hear the enormous steel shaft spinning as it  generates megawatts of electrical power.  

All that electricity flows out to the grid on these  transmission lines to power the surrounding area.

McNary is a run-of-the-river dam, meaning  it doesn’t maintain a large reservoir. It  

stores some water in the forebay to create  the height needed to run the turbines,  

but water flows more or less at the rate it  would without the dam. So, any extra water  

flowing into the forebay that can’t be used for  hydro generation has to be passed downstream  

through one or more of these 22 enormous lift  gates in the spillway beside the powerhouse.

As you can imagine, all this infrastructure  is a lot to operate and maintain. But it’s  

not just hydrologic conditions like floods  and droughts or human needs like hydropower  

demands and irrigation dictating how and when  those gates open or when those turbines run;  

it’s biological criteria too. The  Columbia and its tributaries are home  

to a huge population of migratory fish,  including chinook, coho, sockeye, pink salmon,  

and lampreys, and over the years, through  research, legislation, lawsuits, advocacy,  

and just plain good sense by the powers at be,  we’ve steadily been improving the balance between  

impacts to that wildlife and the benefits of  the infrastructure. In fact, just about every  

aspect of the operation of McNary Dam is driven  by the Fish Passage Plan. This 500-page document,  

prepared each year in collaboration with a litany  of partners, governs the operation of McNary and  

several other dams in the Columbia River system  to improve the survival of fish along the river.

This fish bible includes prescriptive details and  schedules for just about every aspect of the dam,  

including the fish passage structures too.  Usually, when we build infrastructure,  

the people who are going to use it are  actual people. But in a very real sense,  

huge aspects of McNary and other similar dams  are infrastructure for non-humans.  

On top of the hydropower plant and the spillway, McNary  is equipped with a host of facilities meant to  

help wildlife get from one side to the other  with as little stress or injury as possible.  

Let’s look at the fish ladders first.  McNary has two of them, one on each side.

A big contingent of the fish needing past McNary  dam are adult salmon and other species from the  

ocean trying to get upstream to reproduce  in freshwater streams. They are biologically  

motivated to swim against the current, so a fish  ladder is designed to encourage and allow them  

to do just that, and it starts with attraction  water. Dams often slow down the flow of water,  

both upstream and downstream, which can be  disorienting to fish trying to swim against a  

current. Also, dams are large, and fish generally  don’t read signs, so we need an alternative way to  

show them how to get around. Luckily, in  addition to a strong current, salmon are  

sensitive to the sound and motion of splashing  water, so that’s just what we do. At McNary,  

huge electric pumps lift water from the tailrace  below the dam and discharge it into a channel that  

runs along the powerhouse. As the water splashes  back down, it draws fish toward the entrances so  

they can orient with the flow through the ladder.  Some of this was a little tough to understand  

even seeing it in person, so I had a couple  of the engineers at the dam explain it to me.

All these entrances provide options  for the fish to come in, increasing  

the opportunity and likelihood  that they will find their way.

Once they’re in, they make their way upstream  into the ladder itself. Concrete baffles break  

up the insurmountable height of the dam into  manageable sections that fish can swim up at  

their own pace. Most of the fish go through  holes in the baffles, but some jump over the  

weirs. There’s even a window near the top  of the ladder where an expert counts the  

fish and identifies their species.

This data is  important to a wide variety of organizations,  

and it’s even posted online if you  want to have a look. Once at the top,  

the fish pass through a trash rack that keeps  debris out of the ladder and continue their  

journey to their spawning grounds. The goal is that  they never even know they left the river at all,  

and it works. Every year hundreds of thousands  of chinook, coho, steelhead, and sockeye make  

their way past McNary Dam. If you include the  non-native shad, that number is in the millions.

And it’s not just bony fish that find  their way through. Some of the latest  

updates are to help lamprey passage.  These are really interesting creatures!

I’m working on another video that will take a much  deeper look at how this and other fish ladders  

work, so stay tuned for that one, but it’s not the  only fish passage facility here. Because what goes  

up, must come down, or at least their offspring  do (most adult salmon die after reproducing). So,  

McNary Dam needs a way to get those juvenile  fish through as well. That might sound simple;  

thanks to gravity, it’s much simpler to go  down than up. But at a dam, it’s anything but.

I definitely wouldn’t want  to pass through one of these,  

but juvenile fish can make it through  the spillway mostly just fine. In fact,  

specialized structures are often installed  during peak migration times to encourage  

fish to swim through the spillway. McNary Dam has  lift gates where the water flows from lower in the  

water column. But salmon like to stay relatively  close to the surface and they’re sensitive to the  

currents in the flow. Many dams on the Columbia  system have some way to spill water over the top,  

called a weir, that is more conducive to  getting the juveniles through the dam.

The other path for juveniles to take is to be  drawn toward the turbines. But McNary and a lot  

of other dams are equipped with a sophisticated  bypass system to divert the fish before they  

make it that far. and that all starts with the  submersible screens.   

These enormous structures are specially designed with lots of narrow  slots to let as much water through to the  

turbines while excluding juvenile fish. They are  lowered into place with the huge gantry crane that  

rides along the top of the power house. Each  submersible screen is installed in front of a  

turbine to redirect fish upwards while the water  flows continues on. Brushes keep them clean of  

debris to make sure they fish don’t get trapped  against the screen. They might look simple,  

but even a basic screen like this requires a  huge investment of resources and maintenance,  

because they are absolutely critical  to the operation of the dam.

Once the fish have been diverted by the screens,  they flow with some of the water upward into a  

massive collection channel. This was originally  designed as a way to divert ice and debris,  

but now it’s basically a fish cathedral  along the upstream face of the dam.

The juveniles come out in these conduits  from below. Then they flow along the channel,  

while grates along the bottom concentrate them  upward. Next they flow into a huge pipe that pops  

out on the downstream face of the dam. Along the  way, the juveniles pass through electronic readers  

that scan any of the fish that have been equipped  with tags and then into this maze of pipes and  

valves and pumps and flumes. In the past, this  facility was used to store juveniles so they  

could be loaded up in barges and transported  downstream. But over time, the science showed  

it was better to just release them downstream  from the dam. Every once in a while, some of the  

juveniles are separated for counting so scientists  can track them just like the adults in the ladder.  

Then the juveniles continue their journey in the  pipe out to the middle of the river downstream.

Avian predation is a serious problem  for juveniles. Pelicans, seagulls,  

and cormorants love salmon just like the  rest of us. In many cases, most of the fish  

mortality caused by dams isn’t the stress of  getting them through the various structures,  

but simply that birds and other predatory fish take advantage of the  fact that dams can slow down and concentrate  

migrating fish. This juvenile bypass  pipe runs right out into the center  

of the downstream channel where flows are  fastest to give the fish a fighting chance,  

and McNary is equipped with a lot of  deterrents to try and keep the birds away.

All this infrastructure at McNary Dam to help  fish get upstream and downstream has changed  

and evolved over time, and in fact, a lot of  it wasn’t even conceived of when the dam was  

first built. And that’s one of the most  important things I learned touring McNary  

Dam and the Pacific Northwest National Lab:  the science is constantly improving. A ton of  

that science happens here at the PNNL Aquatics  Research Laboratory.  

I spent an entire day just chatting with all the scientists and researchers  here who are advancing the state of the art.

For example, not all the juvenile salmon  get diverted away from those turbines.  

Some inevitably end up going right through. You  might think that being hit by a spinning turbine  

is the worst thing that could happen to a fish,  but actually the change in pressure is the main  

concern. A hydropower turbine’s job is to extract  as much energy as possible from the flowing water.  

In practice, that means the pressure coming  into each unit is much higher than going out,  

and that pressure drop happens rapidly. It doesn’t  bother the lamprey at all, but that sudden change  

in pressure can affect the swim bladder that  most fish use for buoyancy. So how do we know  

what that does to a fish and how newer designs  can be safer? PNNL has developed sensor fish,  

electronic analogues to the real thing that they  can send through turbines and get data out on the  

other side. Compare that data to what we already  know about the limits fish can withstand (another  

area of research at PNNL), and you can quickly and  safely evaluate the impacts a turbine can have.

What’s awesome is seeing how that research  translates into actual investments in  

infrastructure that have a huge effect  on survivability. New turbines recently  

installed at Ice Harbor Dam upstream were  designed in collaboration with PNNL with  

fish passage in mind to reduce injury for  any juveniles that find their way in. One  

study found that more than 98% of fish  survived passing through the new turbines,  

and nearly all the large hydropower dams in  the Columbia river system are slated to have  

them installed in the future. And it’s not just  the turbines that are seeing improvements. I  

talked to researchers who study live fish, how  they navigate different kinds of structures,  

and what they can withstand. Just the engineering  in the water system to keep these fish happy is  

a feat in itself. I talked to a coatings expert  about innovative ways to reduce biological buildup  

on nets and screens. I talked to an energy  researcher about new ways to operate turbines  

to decrease impacts to fish from ramping them up  and down in response to fluctuating grid demands.

And I spent a lot of time learning about how  we track and study the movement of fish as  

they interact with human made structures.  Researchers at PNNL have developed a suite  

of sensors that can be implanted into fish for  a variety of purposes. Some use acoustic signals  

picked up by nearby receivers that can precisely  locate each fish like underwater GPS. Of course,  

if you want to study fish behavior accurately, you  need the fish to behave like they would naturally,  

so those sensors have to be tiny. PNNL has  developed miniscule devices, so small I could  

barely make out the details. You also want to make  sure that inserting the tags doesn’t injure the  

fish, so researchers showed me how you do that  and make sure they heal quickly. And of course,  

those acoustic tags require power, and tiny  batteries (while extremely impressive in their  

own right) sometimes aren’t enough for long-term  studies. So they’ve even come up with fish-powered  

generators that can keep the tags running for  much longer periods of time. A piezoelectric  

device creates power as the fish swims… and  they had some fun ways to test them out too.

Of course, migratory fish aren’t the only part  of the environment impacted by hydropower,  

and with all the competing interests,  I don’t think we’ll ever feel like the  

issue is fully solved. These are messy,  muddy questions that take time, energy,  

and big investments in resources  to get even the simplest answers.

The salmon pink and blue paint in the powerhouse  at McNary really sums it up well, with the blue  

symbolizing the water that drives the station, and  the pink symbolizing the life within the water,  

and its environmental, economic, and cultural  significance. This kind of balancing act is really  

at the heart of what a lot of engineering is all  about. I’m so grateful for the opportunity to see  

and learn more about how energy researchers,  biologists, ecologists, policy experts,  

regulators, activists, and engineers collaborate  to make sure we’re being good stewards of the  

resources we depend on. I think Alison Colotelo,  the Hydropower Program Lead at PNNL put it best:

My crew and I spent two full days in  Washington talking to scientists and  

engineers about these complicated issues.  And I probably learned more about biology  

in those two days than anything  I happened to absorb in college,  

especially about how dams can isolate populations  of fish if they aren’t equipped with well-designed  

passage systems like those at McNary. And  there’s a human equivalent to that too,  

that’s really interesting I think, because we’ve  found ways of living in super remote places,  

and the ways people and fish adapt to those  situations have a lot of similarities. My friend,  

Sam, of the Wendover Productions channel has  a video series called Extremities that is all  

about the most remote places on Earth and how and  why people choose to settle them. I’ve watched all  

15 episodes. They’re so good, and if you want to  check them out, they’re available only on Nebula.

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