Engineers Turn Off Niagara’s American Falls to See What’s Underneath

For several months, one of the world’s most famous waterfalls became a geological work site.

On Thursday, 12 June 1969, the American Falls at Niagara stopped looking like a waterfall.

The Niagara River had not stopped. The Horseshoe Falls had not stopped. But engineers had completed a temporary cofferdam between the New York mainland and Goat Island, diverting the American channel toward the larger Horseshoe Falls.

What remained was an exposed rock face, a mostly dry riverbed and an unusually direct view of everything the water normally concealed.

The operation followed years of concern about erosion and the accumulation of fallen rock at the base of the American Falls. Major rockfalls in the 1930s and 1950s had changed its appearance and raised questions about stability.

The United States Army Corps of Engineers carried out the dewatering project with the cooperation of agencies on both sides of the international boundary.

For several months, one of the world’s most famous waterfalls became a geological work site.

Engineers examined fractures, mapped the exposed bedrock and investigated the talus—the pile of fallen rock at the foot of the falls. Loose and potentially dangerous material was removed from parts of the face, and instruments were installed to monitor movement.

The dry interval also exposed a less scientific accumulation: coins thrown into the water by visitors, along with other objects the river had collected.

The central question was whether the rock pile should be removed to restore a cleaner vertical drop.

Authorities ultimately decided against a dramatic reconstruction. The talus was part of the natural process shaping the falls, and removing it would have required another major intervention without guaranteeing a permanently improved result.

In November, the temporary dam was opened and water returned to the American Falls.

The familiar view resumed, but only after engineers had briefly converted a landmark defined by constant motion into an exposed inspection surface.

They did not turn off Niagara Falls in its entirety.

They did, however, turn off enough of Niagara to see what the waterfall had been hiding.