What’s the Dam Problem
Why it’s so hard to design a fish ladder that works
The salmon look stressed. Behind the algae-streaked windows at Seattle’s Hiram Chittenden fish ladder they’re bumping heads, flipping in the current, and pointing their narrow jaws upstream.
To get to this point, they’ve already swum through the Straits of Juan de Fuca and the Puget Sound, and jumped through the first 17 steps of the ladder, which looks like a skinny set of concrete bleachers. Most fish passes aren’t as visible at the Seattle one, which has an observation deck where you can peer into the steps, but the way the fish have to work around a manmade barrier in the river is common. From here, the fish will keep following the current upstream to spawn in the stream where they were born. Anadramous fish are imprinted, Twilight style, in the rivers where they hatched, so depending on where they came from, they’ll still have several more dams to navigate.
There are more than 80,000 dams in the U.S. and nearly all of them have some kind of fish pass. They range from multi-step ladders like the Seattle one to elevators that suck the fish upstream to nature-like diversion canals. Some of them have been in place since the colonists started farming, and in 1890 the state of Washington passed a law that all dams, “wherever food fish are wont to ascend,” needed to include a fishway. The rest of the country eventually followed suit. Now, any new hydropower dam needs to get its fish ladder design cleared by the Federal Energy Regulatory Commission. But there aren’t a ton of new dams going in, and it’s becoming increasingly clear that just because a ladder exists it doesn’t mean that fish are going to figure out how to use it, or want to.
“We found that, in general, engineered fish ladders have not performed up to everyone’s expectation,” says John Waldman, author of Running Silver: Restoring Atlantic Rivers and Their Great Fish Migrations and a recent study about how migratory fish navigate dams. The numbers from the study were grim. Less than three percent of American shad, for instance, were making it back upstream to their spawning grounds.
All fish migrate to a degree, but dams have the biggest disrupting force on anadramous fish, like salmon or shad, which spawn in rivers but spend most of their lives in the ocean, and catadramous ones, like eel, which live in freshwater, but swim out into the ocean to do it.
There are other factors, like overfishing and climate change, which also hurt declining fish populations, but dams are the most obvious, and because of that, environmental engineers, dam operators, and fish biologists have been trying, with limited success, to design ways for fish to get past them.
In the middle of last century, dams were seen as the answer to a wide range of issues, from water supply to energy security. JFK boosted dam building in his campaign speeches. From the 1920s to the ‘70s, the Army Corps of Engineers built tens of thousands of dams, ones like the Columbia River’s Grand Coulee, which has cut off more access to fish habitat than any other structure in the world. That boom in dam building took a toll. “Many fishways were originally designed for adult salmon over 50 years ago, but we’ve recently found that they don’t work well for other species,” says USGS fish biologist Alexander Haro.
He’s trying to find ways to make them more appealing. At the Conte Anadramous Fish Branch, in Massachusetts, Haro sends fish through a respirometer to see how much energy they exert when they’re stressed, and through what he calls a “sprint swimming flume,” to see how fast they can swim and for how long. “It’s kind of like a high-speed treadmill for fish,” he says. He’ll use that data to try to design fishways that actually work.
The biggest issue, according to Jim Taurek, a NOAA restoration ecologist, is that different fish swim very differently. Some, like salmon, can jump high and sprint, while others — sturgeon for instance — mosey upstream. Alewife freak out in confined spaces and shad don’t like air bubbles.
Because of that, there are almost as many ways to design a passage as there are fish trying to swim through it. “In general, the lower the slope of a fishway, the easier fish can ascend, but that also means the fishway needs to be longer, and many fish will not stay in a fishway structure for very long,” Haro says. It’s possible to have a theoretically perfectly designed ladder that keeps fish stranded on the bottom, because they don’t like its style.
In addition to figuring out the size and shape of the structure you also need to design an appealing entrance, and to make sure the river flow points the fish in the right direction. Salmon can’t use an elevator if they can’t find the door. “Building fish ladders, even thought it’s engineering, it’s also art,” Waldman says.
Then you have to engineer the other side, for downstream fish migration. That’s simpler from a design perspective — the hardest part is teasing the fish out of the main current and into the fish pass — but it can be complicated from the financial side. Running water around the dam is the simplest solution, but utilities make their money on river flows, so they’re hesitant to spill a single drop.
Because of that the workarounds are myriad. Taurek says they’ve tried to truck juvenile fish to less-dammed rivers before they start migrating. That way, when they want to spawn, they come back to the new river. He says it works pretty well, but it’s not cheap and it doesn’t really address the heart of the issue.
Other creative alternatives tend to be expensive, resource intensive (it’s not uncommon for the Department of National Resources to fly fish around dams by helicopter), or slightly crazy. One alternative, Washington-based Whooshh Innovations’ Salmon Cannon (yes, it is exactly what it sounds like), got spoofed on John Oliver’s Last Week Tonight. “Clearly this is the best object that’s ever been invented,” Oliver said, as he launched fish into Jon Stewart’s studio. It seems ridiculous, but the Washington Department of Fish & Wildlife bought one, and started testing it with hatchery fish on the Washougal River in September. Whooshh says it’s less stressful on the fish, and can be used to get them over any height dam, but its actual usability is still unproven.
As the ageing U.S. dams start to break down, and more empirical evidence shows that fish populations are being depleted, there’s been a growing movement to eliminate dams all together. The non-profit advocacy group American Rivers has a whole department dedicated to dam removal. Last year, a documentary, DamNation, won the Audience Choice award at South by Southwest and galvanized environmentalists and river lovers to take down dams, sometimes with Ed Abbey-style monkeywrenching strategies.
There’s weight behind their goals, if not always their techniques. When you get rid of a dam, fish come back, often in exponential numbers and at awesome speeds. When the Edwards Dam on Maine’s Sebasticook River came down in 1999, the alewife population went from zero to three million in 10 years. In 2011, the National Park Service blew up two dams on the Elwha River in Olympic National Park. It was the largest dam removal in history, and now, three years later, Chinook salmon are spawning in upstream habitats for the first time in 100 years.
But it’s not that straightforward, which is why scientists are still trying to design the perfect fish passage. “A lot of people talk a good story, like, ‘Let’s just take that dam out,’” Taurek says. “That’s our preference, but in a lot of cases because of the social challenges, you’ve got to have alternatives.” Aside from power generation — about seven percent of U.S. power comes from hydro and in Washington State it’s as high as 75 percent — many dams are now embedded into the cultural and physical geography around them. We use reservoirs for drinking water, and, especially in old mill towns in the Northeast, the town infrastructure has built up around the dam. Plus, it’s expensive to knock out a dam and rebuild an ecosystem. The Elwha project cost $26.9 million.
So what’s the solution? Given the options, blasting fish over dams in air cannons doesn’t sound quite as outlandish as you might think. Waldman and Taurek advocate for nature-like fishways, meandering streams that go around dams and mimic the native ecosystem. They say they’re the best alternative for fish viability, but, because they need to be low angle, and require a lot of land, they don’t make sense in many situations, especially on high head hydro dams in the West. “I’m not totally anti fish ladder,” Waldman says, “there are some small rivers and streams where fish ladders work great for river herring, but I think all dams should have an existential crisis, to see if they’re really necessary.”
But for now, the only things having existential crises are probably the fish, who are working their way back to where they’re from, thrown off by weirs and ladders. It’s not clear if fish even have feelings, but as the Seattle salmon thrash against the glass, it’s easy to imagine them questioning what kind of madness brought them to this point.
