The Three Gorges Dam is the largest power station in the world and should be benefiting the environment a very great deal. Sure it might cause some setbacks in some areas but I think that people can always improve it later and eventually correct any mistakes they made while constructing it.
Yes, the Three Gorges Dam benefits the environment by creating clean energy. It has a large capacity and helps a lot of people, who would have to find energy by other means. Also, diverting freshwater is a green, responsible use of water, that also benefits a lot of people. The Three Gorges Dam has far more positive benefits for the environment than it has concerns.