I WONDER - How Can Waterfalls Generate Energy?

Waterfalls are not only beautiful but also powerful, providing energy for centuries. Historically, water wheels in mills harnessed this energy, and today, hydroelectric power plants convert the kinetic energy of falling water into electricity. This process, known as hydroelectric power, is a clean and renewable energy source, continuously replenished by nature.

Why is hydroelectric power considered a renewable source of energy?

What does it mean that hydroelectric power is a clean source of energy?