What are the advantages and disadvantages of building large dams of rivers?

Question

What are the advantages and disadvantages of building large dams of rivers?

Answer 1

advantages:  

to use falling water for Hydro electric power]

To give water to big cities since a reservoir is created

to allow tourism and camping around the edges of the lake you made

To provide still water (some animals NEED still water rather than running) for wild life

etc etc

Disadvantages:  

Forests and wildlife are damaged in the beginning of the project

the original river is often diverted and then down-river may be horribly effected by the change in course

Arable land (look up that owrd if you have to) is eaten up by the newly created lake

etc etc

OK??