The highest waterfall in the world is Angel Falls in Venezuela, also known as Kerepakupai Vená ('waterfall of the deepest place') in the local language. These falls are over 3200 feet tall and include an uninterrupted drop of around 2650 feet.
In comparison, the Horseshoe Falls, the highest part of the Niagara Falls group, are 188 feet tall at their highest point. However, the Niagara Falls are considered extraordinary for their width and power. Together, these falls have one of the highest flow rates of any waterfall in the world. More than 6 million cubic feet of water can pass over the Niagara Falls every minute during peak season.
More about waterfalls:
The full description here makes moot my comment -- it isn't height that is impressive; it's the volume.
I learned something new here -- that there is a seasonal flow rate that varies.
In retrospect, yes, in the winter, the falls can freeze up, slowing down.