Yes, just before midnight on March 29, 1848, Niagara residents accustomed to the flow of the Niagara River were awakened when the Niagara River ceased to flow. The reason - a strong south-west wind pushed the ice in Lake Erie in motion. Millions of tonnes of ice became lodged at the mouth of the Niagara River at Lake Erie blocking the channel completely. The self-made dam held the water for approximately thirty hours until the wind shifted and the pent-up weight of the water broke, forcing the Niagara River to flow again.

To prevent this from happening again and to maintain the flow of the Falls for hydro purposes, each year a nearly 3km ice boom is installed at the mouth of the Niagara River at Fort Erie.  Consisting of 22 connected steel pontoons that are anchored to the bottom of the river, the boom greatly reduces the amount of ice that enters the river.

There was only one other time the Falls stopped flowing, from June to November of 1969.  The American Falls were stopped by the U.S. Army Corp of Engineers in order to study what actions, if any, should be taken to remove the debris at the base of the American Falls. Upon completion of the study, it was decided to let nature take its course and to do nothing about rock removal.

Above you can see on the left, what the American Falls looked like when they were turned off, and then on the right what the American Falls look like today.