In 1969, the U.S. turned off Niagara Falls. Here’s what happened next.

In the summer of 1969, America brandished its mastery over nature, landing a man on the Moon. Closer to home—and perhaps to Americans’ hearts—it shut off Niagara Falls.

After major rock collapses in 1931 and 1954, house-sized boulders had built up at the base of the American side of the falls, halving its original vertical drop and prompting concerns that the mighty natural marvel would eventually crumble into one long rapids. In 1965, a local newspaper declared Niagara Falls “an incurably ill loved one,” and subsequent outcry prompted Congress to authorize the U.S. Army Corps of Engineers Corps to study potential renovations to the diminishing natural wonder. The Corps promptly built a cofferdam that diverted the Niagara River over Horseshoe Falls on the Canadian side, shutting off the American Falls completely for diagnosis.

To tourists flocking to Niagara Falls, NY in the summer of 1969, the 100-foot-high dry cliff they encountered instead of the world’s most famous waterfall was stunning proof of American mastery over nature. But it was far from the first time that engineers had attempted to “fix” Niagara Falls—since the late 19th century the Corps and Canadian engineers have continuously tweaked the two cataracts to balance opposing goals: harnessing power and maintaining natural beauty. Today, up to three quarters of the Niagara River runs beneath the falls on both sides of the U.S.-Canada border via massive tunnels to hydroelectric plants, rather than over the towering brinks. Which raises a big question: Is Niagara still worthy of the title “natural” wonder? Or are the falls just a particularly pretty spillway for the hydropower complexes that line Niagara’s shores?

Wilderness becomes industry

First Nations and Native American tribes have lived around Onguiaahra, “the strait,” for at least 10,000 years, and Niagara’s sublime power struck the hearts of the first non-Indigenous explorers (who anglicized the Iroquian name) with a mixture of awe and fear. But where romantics saw beauty, industrialists saw profit. By the mid-1800s, factories and mills had sprung up at the base of the falls on both sides of the international border. In the 1880s, hydroelectric generation was proven at scale for the first time at Niagara and Niagara Falls quickly became global industrial center, according to Daniel Macfarlane, an environmental historian and author of Fixing Niagara Falls.

These developments dismayed Frederick Law Olmsted, the landscape architect who’d designed Central Park in New York City. With Frederick Church, the painter whose depictions of Niagara helped make the falls an American icon, he launched the Free Niagara conservation movement which succeeded in pushing factories away from the base of the falls on both sides of the river.

The first renovations

In 1885 the Olmsted-designed New York State Reservation at Niagara was made the country’s first state park, and quickly became a popular place for tourists and honeymooners to gaze on the wild splendor of the American Falls and larger Horseshoe Falls across the border in Canada. But there was a problem: Niagara Falls was losing its thunder. A growing hydropower “arms race” between the two countries upriver meant less water than ever was flowing over the falls on both sides.

After Canada and the U.S. signed the Niagara River Diversion treaty in 1950, they discussed numerous plans—including turning Niagara into an “intermittent waterfall” that would only run on Sundays— before agreeing to divert no more than half of the Niagara River’s 200,000 cubic feet-per-second natural flow for hydropower during daytime hours during a designated tourist season.

“That means if you were to go to Niagara Falls at Christmastime, or any time in the winter, all you’re seeing is one-quarter of the water going over the waterfall,” Macfarlane tells National Geographic. “The other three quarter is going around [the falls] in diversion tunnels.”

The 1950 treaty also laid out a plan for masking hydropower’s significant impact on the Niagara River and its famous falls. Canadian engineers diverted the river in small sections, blasting and carving the brink of Horseshoe Falls, shrinking it by hundreds of feet to create an unbroken crestline covered by a thin, uniform curtain of water to give the impression of volume. A custom-built “telecolorimeter” helped engineers ensure the falls on the Canadian side remained the right shade of greenish blue. Re-sculpting Horsehoe Fall’s flanks minimized mist, which had been a common tourist complaint.

American preservationists were upset by the geological meddling, but engineers countered by pointing out that Niagara Falls naturally erodes several feet per year anyway—its current location is some eight miles upstream from where water started eating away the Niagara Escarpment about 12,000 years ago.

“But if you have a lot less water going over it, the falls can’t erode as quickly,” Macfarlane explains. What better way to preserve Niagara Falls, the engineers argued, than to simply slow the flow of water over the falls?

The great dewatering

But by the mid-1960s, erosion was a concern again, this time at the American Falls, which also saw declining tourist numbers as more visitors flocked to the Canadian side’s casinos and amusement parks. American officials wanted their falls to get the Horseshoe treatment—a full geological facelift. And they hoped a dewatered waterfall in the meantime would be an irresistible tourist spectacle.

So in 1969, the Army Corps’ Buffalo District set to work, erecting the cofferdam to divert the Niagara River in one fell swoop over just the Horseshoe Falls. Engineers drilled rock cores along the face of the American Falls for Corps geologists to analyze. They ran dye through cracks to see where it emerged. They learned the frequent rock falls were caused by water seeping under the Lockport Dolomite that makes up the brink of the falls and eroding the soft Rochester Shale underneath. A complex sprinkler system kept the delicate rock moist to prevent cracking and extensometers measured rock movement.

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“There are tunnels underneath [the falls], and the rock formations were amazing," recalls U.S. Army Corps of Engineers surveyor Bud Sinnott. "We got to crawl underneath all that stuff where nobody has ever been there before, and maybe never will be again."

Then, it was time to come up with plans to beautify the American Falls and reinforce it against collapse. Engineers sandblasted the riverbed and removed debris, like exacting dentists, to prepare for detailed topographical surveys. Based on those, they built a city-block-sized scale model to test how different configurations of boulders—or talus—at the base of the falls would look, with options for stitching the face of the falls together with cable tendons.

In 1974, the International Joint Commission, the U.S.-Canadian body that governs Niagara Falls, published its final report. Surveys had been sent out with different variations of the American Falls for the U.S. public to choose from: all the talus removed, the talus stacked, flow rates increased, etc. A panel of experts tasked with the final call was unanimous: Do absolutely nothing: no rearranging the talus, no underpinning the falls with concrete or cable stabilizers. The natural processes of erosion that brought the falls to their current location should be embraced, the report declared, and under no circumstance should the falls be made “static and unnatural, like an artificial waterfall in a garden or park, however grand the scale.”

"I would say that there were people disappointed" about the decision to do nothing, says Charles Zernentsch, who worked for the Corps at the time. "I don't think the upper echelon understood it. Because the Corps of Engineers, I believe up high, they wanted to do this. The Corps fixes Niagara Falls? I mean, that was ringing through the halls of Washington, I'm sure, like bells on a reindeer.”

An environmental awakening

What had changed in the decade since the final report on “repairing” the American Falls was commissioned? Everything, according to Macfarlane.

“In between 1965 and 1975, which is when they had been studying this, there was a shift going on within the public and even the engineering profession, about the wisdom maybe of trying to manipulate nature on such a such a large scale,” he explains. In that decade, Americans had “the realization that we can’t control everything, and there’s always unintended consequences.”

By the time the Niagara Falls dewatering project ended, the environmental movement had gone mainstream: America had its first Earth Day, Silent Spring was published, and the public saw the “death of Lake Erie” upstream from Niagara on the news.

By 1970, 700 industrial operations were discharging 250 million gallons of wastewater into the Niagara River every day. Just two miles from the falls, industry had polluted Love Canal so badly that babies were born with birth defects, sparking the environmental justice movement. Renovating Niagara Falls, former symbol of sublime American wilderness, started to look less like ingenuity and more like hubris, Macfarlane says.

A 'natural' Niagara?

So, is Niagara today more natural, or more artificial? To Macfarlane it’s both: infrastructure and nature, a hybrid organic machine, a mechanical waterfall, an “envirotechnology” that our power stations could run dry if we wanted to. The Falls are a paradox, a manmade natural wonder, a carefully sculpted modern version of its historic self.

Ginger Strand, author of Inventing Niagara, has thought about that question a lot. And to her, it’s the wrong one entirely. That question, and the government’s determination to disguise the industrialization and pollution of Niagara, has set us back in our understanding of our place in the world, by reinforcing a made-up divide between technology and nature.

“I think it would have helped if we’d paid attention all along to the fact that we really need to work in collaboration with the natural world, that technology and nature are not separate; they need to cooperate,” she says. “As climate change starts to smack us around more and more, we're becoming more attuned to the fact that we're part of the natural world and not the separate ‘thing’ that just controls it. We're losing our hubris about our control of nature.”

“I think Niagara full force is a natural spectacle,” Strand adds. “And you know, I think the hydro plants are spectacular too.”