06 May 2014: Report

Mimicking Nature, New Designs
Ease Fish Passage Around Dams

Originating in Europe, "nature-like" fishways are now being constructed on some U.S. rivers where removing dams is not an option. Unlike traditional fish ladders, these passages use a natural approach aimed at significantly increasing once-abundant runs of migratory fish.

by rebecca kessler

On a chilly April morning, when the buds had opened just enough to cast a faint red haze on the trees, Jim Turek drove me out to see how his latest construction project was faring after a long winter. In December, work crews completed a project designed to let fish swim over the old Kenyon Mill Dam spanning the Pawcatuck River in Richmond, Rhode Island. The dam, and one that probably preceded it, had been blocking the fish’s path from the sea to their upriver spawning grounds since the 1700s. What was once likely an annual migration of hundreds of thousands of river herring

View Gallery
Kenyon Mill Dam

Rebecca Kessler
A new nature-like fishway at Kenyon Mill Dam is aimed at helping shad and herring make their way up the Pawcatuck River.
and tens of thousands of American shad had dwindled to just a few hundred fish. Runs of Atlantic salmon had long since disappeared.

This was not your typical fish ladder — narrow concrete, metal, or wood contraptions that look a bit like flooded pedestrian highway overpasses. Instead, work crews had installed boulders in sweeping arcs or V-shaped formations clear across the river to create a series of broad pools. These ramped gradually from the natural riverbed up the now nearly submerged 5-foot-tall dam, whose top they had replaced.

The new fishway looked downright pretty, much like a natural swoosh of river, albeit bound on one side by a stone retaining wall and ribbed by a rather orderly series of rapids. In fact, it had been carefully designed to accommodate the particular swimming capabilities and behavioral quirks of shad and herring. These struggling species are critical food for commercial fish stocks along the U.S. East Coast. But there were no fish in sight, even though it was nearly prime migration season. Three dams downstream still blocked fish trying to enter the river, explained Turek, a
Populations of 24 North Atlantic migratory fish species are down to less than 10 percent of their historic size.
restoration ecologist with the U.S. National Marine Fisheries Service (NMFS).

Like the Pawcatuck, U.S. rivers once teemed with diadromous fish, which migrate between the salty ocean and inland freshwater bodies: alewives, blueback herring, shad, salmon, trout, smelt, eels, lamprey, sturgeon, and others. But the installation of thousands of dams, culverts, and other barriers, along with factors like overfishing and pollution, squeezed the fish flow to a trickle. Populations of 24 North Atlantic diadromous fish species are now down to less than 10 percent of their historic size, and half are down to less than 2 percent, by one estimate. New England alone has no fewer than 25,000 dams. Some provide valuable services, like electric power and drinking water. But many are small defunct or failing relicts. Nobody knows exactly how many dams exist across the U.S., but the number may well exceed 1 million, experts say. Roughly half are privately owned, according to the Federal Emergency Management Agency.

Various government agencies and conservation groups are slowly chipping away at the fish passage problem. Everyone agrees that the ideal is to take

Click to Enlarge
Pawcatuck River map

Located in southern Rhode Island, the Pawcatuck River was once barred by six dams, including the Kenyon Mill Dam.
out dams. This provides immediate and permanent improvements in transit for fish and other aquatic life, as well as in water quality and the transport of sediments and nutrients downstream. In the U.S., dam removal is picking up steam. Of the 1,150 U.S. dams removed since 1912, some 850 came out in the last 20 years, according to the conservation group American Rivers. When dams can’t be removed, however, people are increasingly building so-called “nature-like fishways,” such as the one surmounting Kenyon Mill Dam.

Recent research is helping refine the design of these relatively new fishways. They won’t work for every dam, particularly high ones. But experts say that when they’re built right, they should deliver more fish of more species, offer more habitat, and demand less maintenance than traditional fish ladders. And they look better, too.

Turek works to improve diadromous fish passage on rivers throughout New England as part of a nationwide NMFS initiative. He has attended dozens of community meetings to discuss what to do about old dams. Sometimes financial considerations prevent removal of a dam, like the cost of moving a road built on top, dealing with contaminated sediment, or the loss of lakefront property. Other times it's sentimental attachment to a pond or a desire to maintain a historically significant dam.

Kenyon Mill Dam was originally built to power a mill, but its current owner, a textile company, now draws water for fire suppression from its impoundment. Turek says removing the dam — his agency’s first choice on
Many older fish ladders are dysfunctional and data on their overall performance are scarce.
any fish-passage improvement project — could probably have been done for less than two-thirds of the $925,000 construction cost for the more natural fishway. But factors including the possibility that lowering the impoundment’s water level could have adverse effects upriver, particularly on local wells, ultimately led to the choice of a nature-like fishway over dam removal.

Over the years so-called “structural” or “technical” fish ladders and elevators have been appended to a minority of U.S. dams. Many of the designs were developed a century or more ago to aid large, athletic, high-jumping salmon and trout, without a thought for the less-charismatic fish in the river, says Alex Haro, an ecologist with the U.S. Geological Survey. And while some of these ladders work well for certain species in certain situations, Haro says many are dysfunctional, and data on their overall performance are scarce.

“Many of the design criteria for technical fishways up until now have basically been pulled out of a hat or based on anecdotal experience.” Haro says.

A more natural approach to fish passage originated in Europe in the 1970s. The basic idea is to simulate a river with natural materials and flow conditions. Common designs are bypass channels circumventing a dam and rock ramps, like the one at Kenyon Mill Dam. In Europe, nature-like fishways are the preferred solution after dam removal, which is far less common than in the U.S., according to Herman Wanningen of the Netherlands-based company Wanningen Water Consult. Even so, because of higher costs, they still only account for perhaps 20 percent of installed fishways in countries that use them most, Wanningen says. These include the Netherlands, Germany, France, Belgium, Austria, and Switzerland. Recent examples include a newly opened nature-like fishway to help fish and eels over the Herting hydropower dam on Sweden’s Ätran River.

In North America, a few nature-like fishways were completed in the late 1980s and early 1990s, and the approach has gradually gained popularity since, particularly in New England, the Pacific Northwest, Minnesota, and parts of Canada. Nature-like fishways — which also go by names like
'I feel pretty confident that we know what we're doing now,' an ecologist says of fishways.
“roughened channels” and “stream-like fishways” — are catching on elsewhere, too, including Australia, New Zealand, and Japan.

What little hard data there is indicates that the performance of more natural fishways is variable but encouraging, Haro says. For instance, he and three coauthors found that 94 percent of the alewives attempting to pass one New England nature-like fishway made it through, but that only 40 percent managed to traverse another. The poor performer was one of the region’s earliest nature-like fishway projects, and low on the learning curve, Haro says. He believes well-designed projects should approach the 94 percent figure.

Research into the biomechanical and behavioral needs of particular species is helping refine fishway design. Haro runs a unique laboratory in Turners Falls, Massachusetts, with a 120-foot-long hydraulic flume — essentially a model river — where scientists can test how fish navigate various structures under different flow conditions. With NMFS funding, Haro’s team tested around 15 Northeastern diadromous fish species to identify such capabilities as their maximum jumping height and sprint-swimming speed and duration. That helped them determine critical fishway design criteria, such as water velocity and depth, and passageway dimensions. For instance, neither river herring nor shad can jump higher than a foot. And while river herring will dart through small gaps between rocks, shad require larger openings and are easily deterred by turbulence.

This fall, Turek and Haro plan to release design guidelines for nature-like fishways along the East Coast. Guidelines for a few other regions in the U.S. and Europe exist, but without such detailed supporting data on fish capabilities and behavior. “I feel pretty confident that we know what we’re doing now,” Turek says.

Laura Wildman, a Connecticut-based engineer with the environmental consulting firm Princeton Hydro, says she looks first to nature-like fishways when dams can’t come out. Nevertheless she bristles when people
One expert says that building nature-like fishways is “not even close to the benefits of removing a dam.”
suggest a nature-like fishway as a fair compromise between removing a dam and tacking a technical fishway onto it. A chief drawback is that the river remains blocked. “They are not even close to the benefits of something like removing a dam,” Wildman said. “The barrier still exists. The problem still exists. The maintenance issues will exist. … They’re artificial structures.”

Wildman says of nature-like fishways: “They’re still a temporary fix.”

Budgets for improving fish passage are tenuous. But to get serious about restoring migratory fish, Wildman says, government agencies and conservation groups must not only invest more in reconnecting disjointed rivers now, but also start planning decades ahead to decommission fish-blocking structures once the reasons for keeping them expire. “If we


The Ambitious Restoration of
An Undammed Western River

Elwha Dam restoration
With the dismantling of two dams on Washington state’s Elwha River, the world’s largest dam removal project is almost complete. Now, in one of the most extensive U.S. ecological restorations ever attempted, efforts are underway to revive one of the Pacific Northwest’s great salmon rivers.
want to think about sustaining diadromous fish in the long run, we have to have a really big picture [vision] that may seem unrealistic to obtain right now,” she says.

For 20 years Turek has dreamed of reconnecting the Pawcatuck, one of southern New England’s most important migratory fish habitats because of its unpolluted waters and the prime spawning grounds at its head. At the start, six dams barred the 28-mile river. So far, he’s helped make three fish-friendlier. After Kenyon Mill, we stopped at a much-photographed horseshoe-shaped dam sporting new structural fish ladders based on Haro’s data. Then we were off to another nature-like fishway, this one installed to ease fish over steep bedrock where a dam had been removed.

Turek says it will be a few years before something can be done about the three dams downstream that prevent most fish from ever reaching those new passages; one option is their complete removal. Meanwhile, the state is stocking the river to jumpstart the run. If the plan succeeds, Turek says the Pawcatuck’s spring migration could reach 500,000 river herring and 5,000 American shad. Teeming once more, the fish will be a sight to behold. “People never seem to get tired of watching fish runs,” says Turek. “People are mesmerized. ... There’s something therapeutic about it.”

POSTED ON 06 May 2014 IN Biodiversity Business & Innovation Energy Policy & Politics Sustainability Water Europe North America North America 


We're demolishing around 85 dams per year? How many megawatts of power does that represent, annualized? How many windmills/solar farms have to be built to compensate for that energy loss each year, and has the effect on wildlife of these replacements been weighed against that of dam demolition? Has the huge amount of "green technology" mineral and petroleum resources required for constructing non-hydro replacements been considered?

I think it's all too easy to castigate "evil dams" without considering all of the ramifications.
Posted by Greg Durocher on 08 May 2014

Profitable hydro dams are here to stay and that is where fish passage engineers can design effective fish passage. This article did distinguish that the dams that are being removed are generally uneconomical for hydropower or other uses. Many were built for hydro-mechanical power generations ago and are in disrepair. Those dams helped build this country but they are no longer economically viable, and they don't generate annual income to pay for dam repair, install effective fish passage, or address important safety issues. Those are generally the ones being removed to benefit these important fish runs.

So, no, you will not need a bunch more alternative energy projects to make up for lost hydro generation. Each potential dam removal is a case-by-case situation — you are correct they are not all evil but, conversely, they are not all useful. Case-by-case.
Posted by Alan Haberstock on 09 May 2014

How about building the natural fish ladder so that it bypasses the reservoir all together and connects the river above the slack-water down to below the dam so that the migrating fish can travel both up and down river rather than dumping the fish into the artificial lake? Wouldn't that dramatically improve survival rates?

Posted by Brice Campman on 23 Dec 2015


Comments are moderated and will be reviewed before they are posted to ensure they are on topic, relevant, and not abusive. They may be edited for length and clarity. By filling out this form, you give Yale Environment 360 permission to publish this comment.

Email address 
Please type the text shown in the graphic.

rebecca kesslerABOUT THE AUTHOR
Rebecca Kessler is a freelance science and environmental journalist based in Providence, Rhode Island. A former senior editor at Natural History, her work has been published by ClimateCentral.org, Conservation, Discover, Natural History, ScienceNOW, ScienceInsider, and Environmental Health Perspectives. She has previously written for Yale Environment 360 about initiatives to regulate the global aquarium trade and about the endangered North Atlantic right whale.



In Mexico, Fish Poachers Push
Endangered Porpoises to Brink

China’s lucrative black market for fish parts is threatening the vaquita, the world’s most endangered marine mammal. The porpoises, who live only in the Gulf of California, are getting caught up as bycatch in illegal gill nets and killed.

In Japan, a David vs Goliath
Battle to Preserve Bluefin Tuna

A group of small-scale Japanese fishermen are waging an increasingly public struggle against industrial fishing fleets that are using sonar and huge nets to scoop up massive catches of spawning Pacific bluefin tuna.

Unnatural Balance: How Food
Waste Impacts World’s Wildlife

New research indicates that the food discarded in landfills and at sea is having a profound effect on wildlife populations and fisheries. But removing that food waste creates its own ecological challenges.

The Sushi Project: Farming Fish
And Rice in California's Fields

Innovative projects in California are using flooded rice fields to rear threatened species of Pacific salmon, mimicking the rich floodplains where juvenile salmon once thrived. This technique also shows promise for growing forage fish, which are increasingly threatened in the wild.

Northern Forests Emerge
As the New Global Tinderbox

Rapidly rising temperatures, changes in precipitation, and increased lightning strikes are leading to ever-larger wildfires in the northern forests of Alaska, Canada, and Siberia, with potentially severe ecological consequences.


MORE IN Reports

As Drought Grips South Africa,
A Conflict Over Water and Coal

by keith schneider
Facing one of the worst droughts in memory, South Africa’s leaders have doubled down on their support of the water-intensive coal industry. But clean energy advocates say the smartest move would be to back the country’s burgeoning wind and solar power sectors.

Saving Amphibians: The Quest
To Protect Threatened Species

by jim robbins
The decline of the world’s amphibians continues, with causes ranging from fungal diseases to warmer and drier climates. Now, researchers are looking at ways to intervene with triage measures that could help save the most vulnerable populations.

How Rising CO2 Levels May
Contribute to Die-Off of Bees

by lisa palmer
As they investigate the factors behind the decline of bee populations, scientists are now eyeing a new culprit — soaring levels of carbon dioxide, which alter plant physiology and significantly reduce protein in important sources of pollen.

Can Uber-Style Buses Help
Relieve India's Air Pollution?

by jason overdorf
India’s megacities have some the deadliest air and worst traffic congestion in the world. But Indian startups are now launching initiatives that link smart-phone apps and private shuttle buses and could help keep cars and other motorized vehicles off the roads.

Trouble in Paradise: A Blight
Threatens Key Hawaiian Tree

by richard schiffman
The ʻohiʻa is Hawaii’s iconic tree, a keystone species that maintains healthy watersheds and provides habitat for numerous endangered birds. But a virulent fungal disease, possibly related to a warmer, drier climate, is now felling the island’s cherished 'ohi'a forests.

Climate Change Adds Urgency
To Push to Save World’s Seeds

by virginia gewin
In the face of rising temperatures and worsening drought, the world’s repositories of agricultural seeds may hold the key to growing food under increasingly harsh conditions. But keeping these gene banks safe and viable is a complicated and expensive challenge.

As World Warms, How Do We
Decide When a Plant is Native?

by janet marinelli
The fate of a tree planted at poet Emily Dickinson's home raises questions about whether gardeners can — or should — play a role in helping plant species migrate in the face of rising temperatures and swiftly changing botanical zones.

With New Tools, A Focus
On Urban Methane Leaks

by judith lewis mernit
Until recently, little was known about the extent of methane leaking from urban gas distribution pipes and its impact on global warming. But recent advances in detecting this potent greenhouse gas are pushing U.S. states to begin addressing this long-neglected problem.

Is Climate Change Putting
World's Microbiomes at Risk?

by jim robbins
Researchers are only beginning to understand the complexities of the microbes in the earth’s soil and the role they play in fostering healthy ecosystems. Now, climate change is threatening to disrupt these microbes and the key functions they provide.

As Electric Cars Stall, A Move
To Greener Trucks and Buses

by cheryl katz
Low gasoline prices and continuing performance issues have slowed the growth of electric car sales. But that has not stymied progress in electrifying larger vehicles, including garbage trucks, city buses, and medium-sized trucks used by freight giants like FedEx.

e360 digest
Yale Environment 360 is
a publication of the
Yale School of Forestry
& Environmental Studies


Donate to Yale Environment 360
Yale Environment 360 Newsletter



About e360
Submission Guidelines

E360 en Español

Universia partnership
Yale Environment 360 articles are now available in Spanish and Portuguese on Universia, the online educational network.
Visit the site.


e360 Digest
Video Reports


Business & Innovation
Policy & Politics
Pollution & Health
Science & Technology


Antarctica and the Arctic
Central & South America
Middle East
North America

e360 VIDEO

Tribal people and ranchers join together to stop a project that would haul coal across their Montana land.
Watch the video.


The latest
from Yale
Environment 360
is now available for mobile devices at e360.yale.edu/mobile.


An aerial view of why Europe’s per capita carbon emissions are less than 50 percent of those in the U.S.
View the photos.

e360 VIDEO

The 2015 Yale e360 Video Contest winner documents a Northeastern town's bitter battle over a wind farm.
Watch the video.

e360 VIDEO

Food waste
An e360 video series looks at the staggering amount of food wasted in the U.S. – a problem with major human and environmental costs.
Watch the video.

e360 VIDEO

Colorado wildfires
An e360 video goes onto the front lines with Colorado firefighters confronting deadly blazes fueled by a hotter, drier climate.
Watch the video.


A three-part series Tainted Harvest looks at the soil pollution crisis in China, the threat it poses to the food supply, and the complexity of any cleanup.
Read the series.