Human activities on our planet usually have both positive and negative
effects. Often we do things because all we are concerned about is the
positive effects of our actions. We usually dont worry about the 
negative consequences of our actions until it is too late. A perfect
example of this is the building of dams. Dams have been built across 
almost all the major rivers in the world. They are built for many reasons
including flood control, irrigation and power generation. However, 
despite all the positive reasons for building them, there are many
unwanted side effects

I would like you to select one dam, and document it unwanted effects