As you can see, rivers and other bodies of water have a great deal of energy. Where did all this energy begin? What happens when the Sun shines on a puddle? Heat from the Sun changes the water to water vapor. The water vapor goes into the air. Some of it goes up high ano! forms clouds.
Raindrops fall from the clouds. Gravity pulls them down to the Earth. The water keeps falling downward from high places. Rivers flow downhill. Water rushes over cliffs and dams. Gravity makes the water flow from high places to low. This goes on year after year.
All the energy from moving water depends on the Sun. If the Sun stopped shining, no clouds would form, no rain would fall. There would be no way that water could get uphill for gravity to pull it downhill again. There would be no more energy from rivers and waterfalls.
But the Sun does shine. The rain falls. The rivers flow. Water does keep moving. We can keep using the energy from moving water.
