The flow of water was stopped completely over American Falls & Horseshoe Falls on March 29th 1848. "Due to ice in the upper river for several hours. This is the only known time to have occurred. The Falls did not actually freeze over, but the flow was stopped to the point where people actually walked out and recovered artifacts from the riverbed".
People congregate below the Frozen American Falls.
Frozen American Falls.
Frozen Niagara River and the Horseshoe Falls.
On six reported occasions (1883, 1896, 1904, 1909, 1936 and 1947), the water flow over American Falls has been totally froze by ice and didnt flow. But only once has this happened to the much larger Horseshoe Falls (originally known as the Canadian Falls): March 29-31, 1848, the Days Niagara Falls Went Dry".
Source: 1, 2, 3, 4 ,5, 6 & 7
World Leaders (Youth Pictures)