Water is cascading in wide, noisy plumes down the masonry spillway of the Conowingo, a 94-foot hydropower dam spread across the lower Susquehanna River in Maryland. Through the river spray you can make out the fish lift. This is a giant metal tub that every spring rises and falls inside a crisscross of metal scaffolding, delivering upstream-migrating shad and river herring to their spawning grounds above the dam. Fish lifts are of a piece with fish ladders, clever bits of technology that vastly improve the animals’ odds of survival. At least, when the fish are moving in the right direction.

Significantly less successful have been efforts to improve downstream passage through those same dams in the fall. Across the US, huge numbers of fish that need to travel to the ocean to grow or to spawn are chopped to bits as they travel through dams’ fast-spinning turbines.

The U.S. gets about 27 percent of its green energy from hydropower, every electron of which is needed in our race against time to decarbonize. At a unique moment for American hydropower, when much of the 50-plus-year-old old fleet is coming due for updates and relicensing, there’s suddenly a chance to improve hydropower’s sustainability barrier—by reducing the wholesale slaughter of downstream migrating fish. 

Sibling engineers Gia and Abe Schneider are co-founders of Natel Energy, developers of a new turbine that they claim can improve the survival chances of fish from virtually a coin-toss to as much as 100 percent. Natel’s FishSafe Restoration HydroTurbine presents “a phenomenal generational opportunity to modernize our hydropower fleet with turbines that cause less harm,” says Abe.

The problem is that turbines are enormous bladed mechanisms resembling ship propellers. When they spin, usually around 20 to 35 meters per second at their blade tips, they convert a river’s energy into electricity. Fish moving downstream “tend to swim with the main current,” says Jürgen Geist, an aquatic biologist at the Technical University of Munich. ”And in the case of hydropower production, quite often the main current runs through the turbine.”

Fish “can get hit by blades—that’s very intuitive,” says Schneider. They can also get pinched between parts of a turbine. Or subjected to pressure-related barotrauma, which fish biologists equate to a diver with the bends, which can make their swim bladders explode. American eels migrating downstream on the Mississippi and Ottawa rivers in Ontario must pass six hydropower dams and the dangers each one presents before reaching the St. Lawrence River that leads to their spawning site in the Sargasso Sea. There’s currently only a 2.8 percent chance that they’ll make it through intact.

Mass death by turbine wipes out huge numbers of fish that humans like to eat, which is why the Federal Power Act and state laws mandate that dam operators incorporate some type of safe(ish) fish passage to get relicensed. Some dams install screens to keep fish out of turbines and divert them to bypass channels. But not only can many fish squeeze through tight screen grids, they often miss the bypass channels. In one experiment, “Not a single out of more than 1,000 eels used the system,” Geist says. The screens, says Schneider, are also costly to clean and maintain. (Another fish passage technique called trap and haul is arduous and can injure fish.)

Aside from removing unused dams that impede any sort of fish passage and have other ecological negatives currently underway throughout the Northeast—improving survivability through turbines is seen by some experts as the best alternative to bypasses. The U.S. Department of Energy began funding attempts in the 1990s. One design, the Minimum Gap Runner, eliminated two places where fish could get stuck inside a traditional turbine. It had the added advantage of increasing the turbine’s efficiency and has since been adopted by some large West Coast dams. However, the blade is still thin and knife-like, says Schneider. That means a small, juvenile fish can pass un-scathed but a three-foot-long adult eel probably wouldn’t. Another design created a fat leading edge on the blades to minimize pressure drops as fish passed through. This was meant to give them a gentler, less barotraumatic experience, according to Schneider. Where it failed—and why it’s never been installed in any dam—was in its low rotating speed, which also decreased power generation to a money-losing degree.

The Schneiders’ design, which was also supported by funding from DOE, takes the above learnings and tweaks them into a new blade shape whose leading edge is both fat and “swoopy,” as Schneider puts it. The swoop changes the angle of the blade, allowing a fish to glance off it rather than careen into it head-on. Studies show that nine species—American eel, rainbow trout, coho salmon, American shad, alewife, white sturgeon, channel catfish, bluegill, and largemouth bass—have high survival rates. “A lot of our work around testing has been to design turbines that are truly safe across a range of species,” says Gia Schneider.

The Schneiders’ turbines have so far been installed in three small dams under 23-feet-tall and are being monitored for their effect on power output. But the siblings recognize that to achieve meaningful impact, they need proof of concept on a much larger dam—after all, it’s big dams that are responsible for the brunt of U.S. hydropower (the Conowingo in Maryland falls into the class of dams that could accommodate FishSafe). Natel estimates that their turbines could upgrade about 90%of current U.S. hydropower capacity.

The Schneiders are now contracting for a 100-megawatt hydro power plant, which is blocking passage for American eels that have spent as long as 25 years growing to maturity and are ready to migrate back to the Sargasso. That project “will be intensely scrutinized by all the [dam operator’s] peers who operate similar or bigger turbines, and it could really be a game changer,” says Abe Schneider. He expects that even if the current federal administration strips environmental mandates for dam relicensing, the fact that fish such as salmon, eel and shad are important as food means solutions that protect them will remain extremely relevant.   

For all the promise the Schneiders’ FishSafe turbine offers, Geist stresses that every dam and every river and every fish species is distinct, making site-specific testing critical to understanding real-world functionality. His research shows that management changes can be implemented, perhaps alongside safer-turbine installations, to improve outcomes for fish. For example, contrary to conventional wisdom, shutting off one of two or more turbines at a dam site during fall migration season allows more fish to pass safely than minimizing the rotational speed of all the turbines, which has the additional downside of reducing power generation.

David B. Arscott, executive director of the Stroud Water Research Center in Pennsylvania,  says that despite advances in both up- and downstream fish passage, “they’re still not supportive of a free-flowing river and the opportunity for fish to move wherever they want” for their own survival. They also do nothing to improve sediment buildup. Nevertheless, he says, the worsening effects of climate change mean “we need all hands on deck” to keep our planet livable, including continued efforts to switch to more green energy production.

With most of the likeliest rivers in the US already used for electricity generation, any increases in hydropower will have to come from modernizing our current fleet of dams. This presents a rare opportunity to make both ecologists and green energy proponents happy, by giving a much needed boost to hydropower as well as the long-beleaguered denizens of this country’s rivers. 

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Lela Nargi is a journalist covering food and ag policy, social justice, and climate-related science for outlets such as The Guardian, FERN, Eater, and Modern Farmer.