Depending on how long it has been since you have cleaned your sofa, lifting the cushions can be both horrifying and rewarding. You may find a ghastly collection of pet hair, potato chips, and things that could only be described as fuel for nightmares. You might also find a nice collection of coins, that pocket knife you thought you’d never see again, and a long-lost favorite children’s toy.

Over half a century ago, one of Nature’s sofas got a good cleaning when Niagara Falls was temporarily shut down. Nothing you ever retrieved from under your sofa cushions could compare to what engineers discovered when they got a good look at the bottom of the dry falls.

One of the great natural wonders of the world is Niagara Falls. Located on the border between Ontario, Canada, and the state of New York, United States, the impressive geographic spectacle is the effect of Lake Erie draining into Lake Ontario by way of the Niagara River.

Niagara Falls consists of three waterfalls: the Horseshoe Falls, American Falls, and Bridal Veil Falls. Combined, they have the highest flow rate of any waterfall in North America with a vertical drop of more than 50 meters (160 feet). More than 168,000 cubic meters (6 million cubic feet) of water pour over the falls at peak times, dropping 51 meters (167 feet) to the waters below.

The torrent of water is not only beautiful and awe-inspiring, but it also generates an enormous amount of hydroelectric power. The power plants that are fueled by the Falls can generate nearly 4.9 million kilowatts — enough to power 3.8 million homes.

The Falls are vital for the environment, tourism, and commerce. For that reason, authorities monitor its conditions for any signs of trouble. Occasionally, that might involve shutting the water off for inspections and maintenance.

That’s what happened for a few months in 1969. Engineers were concerned that erosion was weakening the American Falls, and they decided they needed to take a closer look.

Shutting the water off to something as significant as a waterfall is obviously more involved than turning off a faucet. To make it happen, engineers built a cofferdam to divert water from the American Falls to the Horseshoe Falls. For three days, over 1,000 trucks hauled over 27,000 tons of rocks and earth to create a temporary structure that stretched 183 meters (600 feet) from the mainland to the head of Goat Island. On June 12, 1969, the water to the American Falls slowed to a trickle. For the first time in nearly 12,000 years, the world was able to take a look at the bottom of the Falls.

Setting aside the geographic features, there were a few things that immediately caught the attention of the workers. For one thing, they found two bodies. As grisly as that was, it was a surprisingly small number. Since 1850, an estimated 5,000 people have gone over the edges of the Falls. The first person to live to tell about the experience did so in 1901. Only 16 are known to have survived (including this fellow, who ultimately was killed by an orange peel).

The human remains that were recovered included a man with brown hair who had been seen jumping into the Falls a few days earlier. The other was a woman with a red dress and a gold ring bearing the inscription “Forget Me Not.” Ironically, no one seems to remember who she was. The cause of death in both cases was attributed to suicide.

Just as when you look under your sofa cushions, once you get past the nastiness, there is generally something good to brighten your day. In this case, engineers found loose change — a lot of it. This 2016 article from Wired reports that engineers found “millions of coins, most of which were removed.” Presumably, these helped fund the cost of the project, but we were unable to find anything that specifically addressed this issue.

With the inspection completed, the cofferdam was removed. On November 25, 1969, the taps were turned on again, and the American Falls roared back to life. Those who witnessed the event considered themselves lucky to be present for such a rare spectacle.

If you are disappointed that you didn’t get the chance to see a portion of Niagara Falls shut down, take courage. You may yet get your chance. In 2016, the New York legislature approved plans to temporarily shut down the Falls once again. This time, it will be to replace bridges near the foot of the Falls. The project is budgeted for $30 million and was slated to begin in 2019. Until the money can be identified, however, the project is on hold.

Once the project starts, we will once again be given the rare privilege of taking another peek under Mother Nature’s sofa cushions. Who knows what we will find this time? Increased tourism over the past fifty years should bring not only more coins, but sunglasses, cell phones, cameras, camcorders, and flip flops.

On a positive note, no one has been reported to have jumped in the Falls since 1969 who hasn’t been recovered. Hopefully, there won’t be any gruesome surprises this time around.