Water at the top of Iagara Falls possesses gravitational potential energy
because of its height, and kinetic energy because of its motion.
A lot of this energy is tapped off of the stream as the water falls, and is
used to generate electrical energy.
180-ft = about 54.9 meters
1 kilogram (1 liter) of water loses about
(1 kg) x (9.8 m/s²) x (54.9 m)
= about 538 joules of potential energy,
while falling from the top of Iagara Falls
to the pool at the bottom.