In 2006, China completed construction of the Three Gorges Dam, which sits on the Yangtze River. The dam is the largest hydroelectric river dam in the world. Building it, though, forced more than one million people to move to new towns and villages. The dam has also caused other problems. Scientists say the dam has harmed several hundred types of plants and animals because the reservoir destroyed the environment in which they lived. Water from the reservoir has leaked into the ground, making it easier for rocks and earth to fall down. This has created landslides, forcing even more people to move. Farther down the Yangtze, people are not getting as much water from the river as they once did. At the same time, more salt water is entering the area where the river meets the sea. Some sea creatures that live in salt water can now live farther upstream in the Yangtze. They are eating the eggs of other kinds of river life. Scientists still do not know all the damage the dam could cause in years to come.