The flow of water going over the falls has been drasticly reduced and almost stopped on several occassions with the last time being in 1969.
In the 1969 case the Army Corps of Engineers stopped the water coming over the American Falls in order to determine if the large collection of Rocks at the bottom could be removed however they felt that this would only damage the falls more so the rocks were left.
A portion of the Horseshoe Falls was stopped in 1953 in order to correct the flow of water over the crest of the Falls.
Before these dates the falls have stopped due to large ice jams building up in Lake Erie and reducing water flow into the Niagara River.
Since 1969 the Falls have not been stopped for any reason at. The water flowing over the edge, as powerful as it seems , is only a fraction of what used to be due to the industrial and hydro needs of both countries. For these reasons there is very little erosion and therefore little need for maintenance or repair.
