Every autumn, something ancient slips down the St. Lawrence River toward the sea.
These are the oldest eels in the watershed, finally ready to spawn.
To reach the Atlantic, they have to pass through a wall of spinning steel.
For decades, a measured share of them has not made it through alive.
That loss has long been treated as part of the price of making power from moving water.
A new blade shape is rewriting that math.
Why a thin blade kills and a blunt one does not
An eel’s body is long, slender and flexible, which makes it unusually vulnerable to a spinning turbine blade. A conventional blade has a thin, knife like leading edge built to slice through water with maximum efficiency. That same sharp edge can sever or crush a fish caught in its path as it sweeps past.
The new design flips that logic. Engineers gave the runner a thick, blunt leading edge and a more curved blade shape, so a strike becomes a glancing shove rather than a cut.
The second change is smaller but just as important. The gap between the blade and its housing is minimized, since that narrow space is where a long body can get pinned and torn, and the design also removes the converging pinch points where blades meet the hub.
A dam that two countries share, and a fish that has to cross it
The setting is the Robert Moses-Robert H. Saunders Power Dam, which spans the St. Lawrence River between Massena, New York, and Cornwall, Ontario. The American half is the St. Lawrence-Franklin D. Roosevelt Power Project, run by the New York Power Authority; the Canadian half is the R.H. Saunders station.
On the American side alone, the plant is serious infrastructure. Its 16 turbines produce over 900 MW of electricity, enough, the turbine developer says, to light a city the size of Washington, DC.
The eels using this stretch of river are not a random sample. They are overwhelmingly breeding females, so losing them at the dam does not just remove individuals, it removes the next generation before it ever spawns.
The number everyone quoted, and the one now proposed to replace it
For years the accepted figure at this site was grim. Field work in the late 1990s put turbine passage mortality at about 26 percent, roughly one in four full grown females, and eels that then pass the Beauharnois station downstream face a cumulative loss estimated near 40 percent.
A feasibility study now puts a different number on the table, carried out by the turbine developer with the plant operator and funded by a federal fish research fund rather than an independent lab.
The work used computational fluid dynamics on replacement runner designs, and predicted eel blade strike survival above 98 percent across all simulated operating conditions. A later company update put the projection at over 98.5 percent, at matched efficiencies and with no lost generation.
The power side held up too. At a gross head of about 82 feet, predicted peak efficiencies of 94.6 and 94.3 percent fell inside the measurement uncertainty of the existing units, with projected annual energy within half a percent of current output.
Why nobody had tried this fix here before
This is not the first attempt at solving the eel problem here. A fish friendly turbine was evaluated at this dam in the mid 2000s and ruled out because of the extensive reconstruction it would have required.
What makes the new proposal different is that it fits inside the existing machine as an in place replacement, needing no changes to the dam, the powerhouse or plant operations, built with conventional manufacturing methods.
That single detail turns an engineering dream into something a utility can actually schedule, the same logic behind the sun tracking panels at Illinois’ Energy Farm, arranged to share working farmland rather than replace it.
Lake sturgeon, mooneye, walleye, northern pike and muskellunge are also expected to gain from improved turbine passage, so a retrofit built around one vulnerable traveler could protect a whole river’s worth of fish sharing the same narrow gate.
What still has to prove itself before the blades ever spin
The survival figure comes from a model rather than a river, and from the company that would sell the hardware. No such runners have been installed at this dam, and the next step is turning simulation into steel bolted into a real powerhouse, the same leap tested in a separate turbine trial, where a fish the length of a pencil swam past spinning blades and came out alive.
There is live animal evidence behind the blade shape too. A peer reviewed study passed 131 American eels through a scaled version of the same runner and recorded 100 percent survival over a 48 hour holding period, with later trials at higher blade speeds reporting 99.2 percent.
None of that erases the decades when roughly a quarter of the river’s breeding females did not finish the trip. But a blade shape reshaped from thin to blunt may finally let an ancient migration survive a modern machine built to sit squarely in its path.
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