Hydroelectricity is a way to make electricity by using water. In Japan, there are many mountains, and these mountains have rivers that flow from them. There are dams built on these rivers, and when the water flows down from the mountains, it flows through these dams.
When the water flows through these dams, it spins big turbines. These turbines are like big wheels that turn and create electricity. That's how hydroelectricity is made in Japan!
It's important because Japan needs electricity to power things like lights, computers, and TVs. So, hydroelectricity is a clean and renewable way to create power, which means Japan can use it over and over again, without worrying about running out of energy.
Plus, it's really cool to see these huge turbines spinning and turning the energy from water into electricity!