Niagara Falls has been changing very rapidly.
If you look at timestamps just over the past 500 years, you can see the movement.
Notice in the lines above, that it didn’t always have its famous horseshoe shape. That happened due to the lower density on the outer layers of the rock.
The overall recession is because of obvious reasons, water wearing away on the ledges of the falls. But also because of constant weather changes in that region that accelerate that erosion.
In the past 10,000 years, the base of the waterfall has moved more than 7 miles. That might seem like a really long distance, given how small the change is in the above picture—the reason is due to the limestone rock which the waterfall has now reached.
Prior to reaching this stone, and after it—the waterfall will recede much faster than it is now as it gets to the softer ground to erode. (Source: Rate Of Erosion Of Niagara Falls. Marriott on the falls)
In any event, if you ever get the chance, you should surely visit the falls.