Imagine running water in a river, just like a stream. It moves very fast and very strong. But sometimes people want to store the water so they build a wall in the river called a dam. This makes the water stop moving fast, and it makes a pond or lake behind the dam. Sometimes people build a dam because they need the water for things like drinking or farming.
But sometimes, dams can cause problems for the animals and plants that live in the river. When the dam stops the water, it can change how the river flows, and it makes it harder for fish and other animals to move around. Some animals might not like the still water behind the dam and may not be able to survive like they used to.
Sometimes people decide they want to take the dam out of the river to help fix these problems. It's kind of like taking down a big wall. When people take away the dam, the river can go back to how it used to be. The water starts moving fast again and it can help the animals and plants that live in and around the river. So, taking out the dam can be good for the environment and the animals that call the river home.