Changing a river into a lake is basically what a large dam does. One reason we do this to create reservoirs of fresh water. However, dams change the local ecosystem in a big way. What is one negative impact of building a dam

One negative impact of building a dam could be that it affects natural habitats of animals who live in and around the river. When you build a dam, the river's height becomes smaller because a huge amount of water becomes technically removed or blocked. This can affect animals such as fish or beavers or anyone who needs that water.